Capitalize first letter of each word of input

CJam, 15 13 bytes

Lq{_eu?_S-}/;

Try it online in the CJam interpreter.

Pseudocode

L             e# B := ""
 q            e# Q := input()
  {       }/  e# for C in Q:
   _eu?       e#     C := B ? C : uppercase(C)
       _S-    e#     B := string(C).strip(" ")
            ; e# discard(B)

All modified characters C are left on the stack and, therefore, printed when exiting.

CSS 2.1, 49

:after{content:attr(t);text-transform:capitalize}

Explanation:

• The attr function takes the input from a t (text) HTML attribute.
• The input is capitalized by setting text-transform to capitalize.
• The output is provided as a generated content, using the content property on an ::after pseudo-element.

Runnable snippet:

:after {
    content: attr(t);
    text-transform: capitalize;
}

<div t="eCommerce rocks. crazyCamelCase stuff. _those  pigeon-toed shennanigans. Fiery trailblazing 345 thirty-two Roger. The quick brown fox jumped over the lazy dogs. Clancy Brown would have been cool as Lex Luthor. good_bye"></div>

Note: CSS 2.1 specified the desired behavior: capitalize uppercased the first character of each word. However, CSS3 uppercases first typographic letter unit of each word. So the snippet above won't work properly neither on old IE, which didn't follow CSS 2.1; nor on new compliant browsers which follow CSS3.

Javascript (ES6), 77 bytes

alert(prompt().split(' ').map(x=>x&&x[0].toUpperCase()+x.slice(1)).join(' '))

Commented

alert( // output
    prompt(). // take input
    split(' '). // split by spaces
    map(x=> // map function to array
        x && // if x, empty string "" is falsey and returns itself
        x[0].toUpperCase() + x.slice(1) // capaitalize 1st char and concatenate the rest
    ).
    join(' ') // join array with spaces
)