Setting up buttons in SKScene

you could use a SKSpriteNode as your button, and then when the user touches, check if that was the node touched. Use the SKSpriteNode's name property to identify the node:

//fire button
- (SKSpriteNode *)fireButtonNode
{
    SKSpriteNode *fireNode = [SKSpriteNode spriteNodeWithImageNamed:@"fireButton.png"];
    fireNode.position = CGPointMake(fireButtonX,fireButtonY);
    fireNode.name = @"fireButtonNode";//how the node is identified later
    fireNode.zPosition = 1.0;
    return fireNode;
}

Add node to your scene:

[self addChild: [self fireButtonNode]];

Handle touches:

//handle touch events
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    UITouch *touch = [touches anyObject];
    CGPoint location = [touch locationInNode:self];
    SKNode *node = [self nodeAtPoint:location];

    //if fire button touched, bring the rain
    if ([node.name isEqualToString:@"fireButtonNode"]) {
         //do whatever...
    }
}

For people writing their games in Swift! I have rewritten the essential parts of Graf's solution to a swift class. Hope it helps:

import Foundation
import SpriteKit

class FTButtonNode: SKSpriteNode {

    enum FTButtonActionType: Int {
        case TouchUpInside = 1,
        TouchDown, TouchUp
    }

    var isEnabled: Bool = true {
    didSet {
        if (disabledTexture != nil) {
            texture = isEnabled ? defaultTexture : disabledTexture
        }
    }
    }
    var isSelected: Bool = false {
    didSet {
        texture = isSelected ? selectedTexture : defaultTexture
    }
    }
    var defaultTexture: SKTexture
    var selectedTexture: SKTexture

    required init(coder: NSCoder) {
        fatalError("NSCoding not supported")
    }

    init(normalTexture defaultTexture: SKTexture!, selectedTexture:SKTexture!, disabledTexture: SKTexture?) {

        self.defaultTexture = defaultTexture
        self.selectedTexture = selectedTexture
        self.disabledTexture = disabledTexture

        super.init(texture: defaultTexture, color: UIColor.whiteColor(), size: defaultTexture.size())

        userInteractionEnabled = true

        // Adding this node as an empty layer. Without it the touch functions are not being called
        // The reason for this is unknown when this was implemented...?
        let bugFixLayerNode = SKSpriteNode(texture: nil, color: nil, size: defaultTexture.size())
        bugFixLayerNode.position = self.position
        addChild(bugFixLayerNode)

    }

    /**
    * Taking a target object and adding an action that is triggered by a button event.
    */
    func setButtonAction(target: AnyObject, triggerEvent event:FTButtonActionType, action:Selector) {

        switch (event) {
        case .TouchUpInside:
            targetTouchUpInside = target
            actionTouchUpInside = action
        case .TouchDown:
            targetTouchDown = target
            actionTouchDown = action
        case .TouchUp:
            targetTouchUp = target
            actionTouchUp = action
        }

    }

    var disabledTexture: SKTexture?
    var actionTouchUpInside: Selector?
    var actionTouchUp: Selector?
    var actionTouchDown: Selector?
    weak var targetTouchUpInside: AnyObject?
    weak var targetTouchUp: AnyObject?
    weak var targetTouchDown: AnyObject?

    override func touchesBegan(touches: NSSet!, withEvent event: UIEvent!)  {
        let touch: AnyObject! = touches.anyObject()
        let touchLocation = touch.locationInNode(parent)

        if (!isEnabled) {
            return
        }
        isSelected = true
        if (targetTouchDown != nil && targetTouchDown!.respondsToSelector(actionTouchDown!)) {
            UIApplication.sharedApplication().sendAction(actionTouchDown!, to: targetTouchDown, from: self, forEvent: nil)
        }


    }

    override func touchesMoved(touches: NSSet!, withEvent event: UIEvent!)  {

        if (!isEnabled) {
            return
        }

        let touch: AnyObject! = touches.anyObject()
        let touchLocation = touch.locationInNode(parent)

        if (CGRectContainsPoint(frame, touchLocation)) {
            isSelected = true
        } else {
            isSelected = false
        }

    }

    override func touchesEnded(touches: NSSet!, withEvent event: UIEvent!) {

        if (!isEnabled) {
            return
        }

        isSelected = false

        if (targetTouchUpInside != nil && targetTouchUpInside!.respondsToSelector(actionTouchUpInside!)) {
            let touch: AnyObject! = touches.anyObject()
            let touchLocation = touch.locationInNode(parent)

            if (CGRectContainsPoint(frame, touchLocation) ) {
                UIApplication.sharedApplication().sendAction(actionTouchUpInside!, to: targetTouchUpInside, from: self, forEvent: nil)
            }

        }

        if (targetTouchUp != nil && targetTouchUp!.respondsToSelector(actionTouchUp!)) {
            UIApplication.sharedApplication().sendAction(actionTouchUp!, to: targetTouchUp, from: self, forEvent: nil)
        }
    }

}

I've made my own Button-Class that I'm working with. SKButton.h:

#import <SpriteKit/SpriteKit.h>
@interface SKButton : SKSpriteNode

@property (nonatomic, readonly) SEL actionTouchUpInside;
@property (nonatomic, readonly) SEL actionTouchDown;
@property (nonatomic, readonly) SEL actionTouchUp;
@property (nonatomic, readonly, weak) id targetTouchUpInside;
@property (nonatomic, readonly, weak) id targetTouchDown;
@property (nonatomic, readonly, weak) id targetTouchUp;

@property (nonatomic) BOOL isEnabled;
@property (nonatomic) BOOL isSelected;
@property (nonatomic, readonly, strong) SKLabelNode *title;
@property (nonatomic, readwrite, strong) SKTexture *normalTexture;
@property (nonatomic, readwrite, strong) SKTexture *selectedTexture;
@property (nonatomic, readwrite, strong) SKTexture *disabledTexture;

- (id)initWithTextureNormal:(SKTexture *)normal selected:(SKTexture *)selected;
- (id)initWithTextureNormal:(SKTexture *)normal selected:(SKTexture *)selected disabled:(SKTexture *)disabled; // Designated Initializer

- (id)initWithImageNamedNormal:(NSString *)normal selected:(NSString *)selected;
- (id)initWithImageNamedNormal:(NSString *)normal selected:(NSString *)selected disabled:(NSString *)disabled;

/** Sets the target-action pair, that is called when the Button is tapped.
 "target" won't be retained.
 */
- (void)setTouchUpInsideTarget:(id)target action:(SEL)action;
- (void)setTouchDownTarget:(id)target action:(SEL)action;
- (void)setTouchUpTarget:(id)target action:(SEL)action;

@end

SKButton.m:

#import "SKButton.h"
#import <objc/message.h>


@implementation SKButton

#pragma mark Texture Initializer

/**
 * Override the super-classes designated initializer, to get a properly set SKButton in every case
 */
- (id)initWithTexture:(SKTexture *)texture color:(UIColor *)color size:(CGSize)size {
    return [self initWithTextureNormal:texture selected:nil disabled:nil];
}

- (id)initWithTextureNormal:(SKTexture *)normal selected:(SKTexture *)selected {
    return [self initWithTextureNormal:normal selected:selected disabled:nil];
}

/**
 * This is the designated Initializer
 */
- (id)initWithTextureNormal:(SKTexture *)normal selected:(SKTexture *)selected disabled:(SKTexture *)disabled {
    self = [super initWithTexture:normal color:[UIColor whiteColor] size:normal.size];
    if (self) {
        [self setNormalTexture:normal];
        [self setSelectedTexture:selected];
        [self setDisabledTexture:disabled];
        [self setIsEnabled:YES];
        [self setIsSelected:NO];

        _title = [SKLabelNode labelNodeWithFontNamed:@"Arial"];
        [_title setVerticalAlignmentMode:SKLabelVerticalAlignmentModeCenter];
        [_title setHorizontalAlignmentMode:SKLabelHorizontalAlignmentModeCenter];

        [self addChild:_title];
        [self setUserInteractionEnabled:YES];
    }
    return self;
}

#pragma mark Image Initializer

- (id)initWithImageNamedNormal:(NSString *)normal selected:(NSString *)selected {
    return [self initWithImageNamedNormal:normal selected:selected disabled:nil];
}

- (id)initWithImageNamedNormal:(NSString *)normal selected:(NSString *)selected disabled:(NSString *)disabled {
    SKTexture *textureNormal = nil;
    if (normal) {
        textureNormal = [SKTexture textureWithImageNamed:normal];
    }

    SKTexture *textureSelected = nil;
    if (selected) {
        textureSelected = [SKTexture textureWithImageNamed:selected];
    }

    SKTexture *textureDisabled = nil;
    if (disabled) {
        textureDisabled = [SKTexture textureWithImageNamed:disabled];
    }

    return [self initWithTextureNormal:textureNormal selected:textureSelected disabled:textureDisabled];
}




#pragma -
#pragma mark Setting Target-Action pairs

- (void)setTouchUpInsideTarget:(id)target action:(SEL)action {
    _targetTouchUpInside = target;
    _actionTouchUpInside = action;
}

- (void)setTouchDownTarget:(id)target action:(SEL)action {
    _targetTouchDown = target;
    _actionTouchDown = action;
}

- (void)setTouchUpTarget:(id)target action:(SEL)action {
    _targetTouchUp = target;
    _actionTouchUp = action;
}

#pragma -
#pragma mark Setter overrides

- (void)setIsEnabled:(BOOL)isEnabled {
    _isEnabled = isEnabled;
    if ([self disabledTexture]) {
        if (!_isEnabled) {
            [self setTexture:_disabledTexture];
        } else {
            [self setTexture:_normalTexture];
        }
    }
}

- (void)setIsSelected:(BOOL)isSelected {
    _isSelected = isSelected;
    if ([self selectedTexture] && [self isEnabled]) {
        if (_isSelected) {
            [self setTexture:_selectedTexture];
        } else {
            [self setTexture:_normalTexture];
        }
    }
}

#pragma -
#pragma mark Touch Handling

/**
 * This method only occurs, if the touch was inside this node. Furthermore if 
 * the Button is enabled, the texture should change to "selectedTexture".
 */
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    if ([self isEnabled]) {
        objc_msgSend(_targetTouchDown, _actionTouchDown);
        [self setIsSelected:YES];
    }
}

/**
 * If the Button is enabled: This method looks, where the touch was moved to.
 * If the touch moves outside of the button, the isSelected property is restored
 * to NO and the texture changes to "normalTexture".
 */
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
    if ([self isEnabled]) {
        UITouch *touch = [touches anyObject];
        CGPoint touchPoint = [touch locationInNode:self.parent];

        if (CGRectContainsPoint(self.frame, touchPoint)) {
            [self setIsSelected:YES];
        } else {
            [self setIsSelected:NO];
        }
    }
}

/**
 * If the Button is enabled AND the touch ended in the buttons frame, the
 * selector of the target is run.
 */
- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
    UITouch *touch = [touches anyObject];
    CGPoint touchPoint = [touch locationInNode:self.parent];

    if ([self isEnabled] && CGRectContainsPoint(self.frame, touchPoint)) {
        objc_msgSend(_targetTouchUpInside, _actionTouchUpInside);
    }
    [self setIsSelected:NO];
    objc_msgSend(_targetTouchUp, _actionTouchUp);
}

An example: To initialize a button, you write the following lines:

    SKButton *backButton = [[SKButton alloc] initWithImageNamedNormal:@"buttonNormal" selected:@"buttonSelected"];
    [backButton setPosition:CGPointMake(100, 100)];
    [backButton.title setText:@"Button"];
    [backButton.title setFontName:@"Chalkduster"];
    [backButton.title setFontSize:20.0];
    [backButton setTouchUpInsideTarget:self action:@selector(buttonAction)];
    [self addChild:backButton];

Furthermore you need the 'buttonAction' method in your class. * No warranty that this class is working right in every case. I'm still quite new to objective-c. *

If you think having to do this is annoying and pointless you can disable the check in the build settings by setting 'Enable strict checking of objc_msgSend Calls' to 'No'