Generate all possible integers

Javascript (E6) 215 (315 - 2*50 bonus) 252

Edit Simplified. Correct bug of 0 missing

Defined as a function, then counting 10 more byte for output using alert()

Important Really this one is not valid according to the rules, because javascript can not handle big numbers. For instance with parameters 2,5 it can't find 2^2^2^2^2 (ie 2^65536). A number this big is 'Infinity' in javascript.

Golfed

F=(n,k,g={})=>{k+=k-1;for (l=i=1;x=i.toString(6),l+=!!x[l],l<k;i++)if(x.split(0).length*2==l+1){for(s=[n,n],p=l;o=x[--p];)
if(-o)b=s.pop(),a=s.pop(),s.push(o<2?a+b:o<3?a-b:o<4?a*b:o<5?a/b:Math.pow(a,b));else s.push(x[p]=n);
r=Math.floor(s.pop());r>=0&isFinite(r)&!isNaN(r)&!g[r]&&(g[r]=x)}return Object.keys(g)};

To be golfed. I have an idea I want to share: use a postfix notation. In postfix any type of expression is made just of values and operators - no parentheses needed. The postfix notation can be translated to usual algebraic infix notation - but that's out of scope in this challenge.

Usage

alert(F(4,3))

Output 1,2,3,4,5,8,12,16,20,32,64,252,256,260,1024,4096,65536,4294967296,1.3407807929942597e+154

Ungolfed

F=(n, k, g={})=>{
  k += k - 1;
  // Count in base 6 - '0' means Value, '1'..'5' means operators
  // A valid expression starts with Value twice, then n operators intermixed with n-1 Values
  // x: Coded expression, l: Expression length, k Expression limit length from param
  for (l = i = 1; x = i.toString(6), l += !!x[l], l<k; i++)
    if (x.split(0).length*2 == l+1) // check balancing values/operators
    {
      for (s = [n,n], p = l; o = x[--p];) // Calc stack starts with N,N
        if (-o) // If not '0'
          b=s.pop(),a=s.pop(), // Do calc
          s.push(o<2 ? a+b : o<3 ? a-b : o<4 ? a*b : o<5 ? a/b : Math.pow(a,b))
        else // Push value 
          s.push(n) // 
      r = Math.floor(s.pop()); // Last result in stack
      r >= 0 & isFinite(r) & !isNaN(r) & !g[r] && (g[r]=x) // Put in hashtable avoiding duplicates
    }
  // Uncomment this to see the postfix expression list 
  // for (i in g) console.log(i, [n,n,...[...g[i]].reverse().map(v=>v>0?'x+-*/^'[v]:n)])
  return Object.keys(g) // Retust list of hashtable keys
}

First version this is more complicated but maybe easier to follow

Display the postfix expression for each number

F=(n,k)=> {
  var i,l,s;
  var cmd;
  var op='n+-*/^'
  var bag = {}
  function Calc(val,pos,stack)
  {
    while (c = cmd[pos])
    {
        if (c == 0)
        {
            stack.push(n);
            cmd[pos] = n
            pos++
        }
        else 
        {
            var b=stack.pop(), a=stack.pop();
            stack.push(c < 2 ? a+b : c < 3 ? a-b : c < 4 ? a*b : c < 5 ? a/b
               : Math.pow(a,b))
            cmd[pos]=op[c]
            pos++
        }
    }
    var res = Math.floor(stack.pop())
    if (res > 0 && isFinite(res) && !isNaN(res) && !bag[res]) 
    {
       bag[res] = cmd
    }
  }
  k=k+k-3;
  for (i=1;s=i.toString(6), !s[k]; i++)
  {
       l=s.split(0).length;
       if (l+l-1==s.length) 
       {
          var cmd = (s+'00').split('').reverse()
          Calc(n, 0, [], cmd.map(c=>op[c]).join(' '))
       }
  }

  for (i in  bag)
  {
    console.log(bag[i],'=', i)
  }
}

Usage

F(4,3)

Output

[4, 4, "/"] = 1
[4, 4, "+", 4, "/"] = 2
[4, 4, 4, "/", "-"] = 3
[4, 4, "-", 4, "+"] = 4
[4, 4, "/", 4, "+"] = 5
[4, 4, "+"] = 8
[4, 4, "+", 4, "+"] = 12
[4, 4, "*"] = 16
[4, 4, "*", 4, "+"] = 20
[4, 4, "+", 4, "*"] = 32
[4, 4, "*", 4, "*"] = 64
[4, 4, "^", 4, "-"] = 252
[4, 4, "^"] = 256
[4, 4, "^", 4, "+"] = 260
[4, 4, "^", 4, "*"] = 1024
[4, 4, "+", 4, "^"] = 4096
[4, 4, "*", 4, "^"] = 65536
[4, 4, "^", 4, "^"] = 4294967296
[4, 4, 4, "^", "^"] = 1.3407807929942597e+154

Python 2, 249 characters - 50 bonus = 199

from operator import*
n,k=input()
def g(a):
 if len(a)==1:yield a[0]
 else:
  for i in range(1,len(a)):
   for l in g(a[:i]):
    for r in g(a[i:]):
     for o in[add,sub,mul,pow]:
      yield o(l,r)
     if r:yield l/r
print set(map(abs,g([n]*k)))

Sample runs:

2,2
set([0, 1, 4])
4,3
set([32, 65536, 2, 3, 4, 5, 0, 1, 64, 252, 13407807929942597099574024998205846127479365820592393377723561443721764030073546976801874298166903427690031858186486050853753882811946569946433649006084096L, 12, 1024, 4096, 20, 4294967296L, -252, -12, -4, -3, 260])

This claims the exponentiation bonus of -50 points. Allowing exponentiation can give some staggeringly large results for small inputs (remove pow from the list of operators to try without exponentiation).

Mathematica, 105 bytes - 100 bonus = 5

Note: This does not currently support parentheses. Fixing once the OP clarifies the challenge.

If negative integers are okay, too, this scores 1 instead.

f[n_,k_]:=Union@Abs@Floor@ToExpression[ToString@n&~Array~k~Riffle~#<>""&/@Tuples[Characters@"*+/-^",k-1]]

Somewhat ungolfed:

f[n_, k_] :=
 Union@Abs@Floor@
    ToExpression[
     ToString@n &~Array~k~Riffle~# <> "" & /@
      Tuples[Characters@"*+/-^", k - 1]
     ]

I'm claiming both bonuses for including exponentiation and flooring non-integer results.

Examples:

f[2, 2]
f[4, 3]

Out[1] = {0, 1, 4}
Out[2] = {0, 3, 4, 5, 12, 20, 64, 252, 260, 1024, 13407807929942597099574024998205846127479365820592393377723561443721764030073546976801874298166903427690031858186486050853753882811946569946433649006084096}