Extends jQuery via prototype to capitalize the first letter of each word in a sentence ('all'), just the first word in a sentence (default), or title text ('title' - capitalizes each word in the sentence minus words like "the", "and", "or", "but" etc. Usage included under code.

jquery.capitalize.js

String.prototype.capitalize = function(type) {
    var array, capitalized, doNotCapitalize;

    // if type = all, capitalize first letter of each word
    if(type === 'all'){
        array		= this.split(' '); // split on spaces
        capitalized	= '';

        $.each(array, function( index, value ) {
            capitalized += value.charAt(0).toUpperCase() + value.slice(1);

            if( array.length != (index+1) )
                capitalized += ' '; // add a space if not end of array
        });
        return capitalized;
    }

    // if type = title, capitalize first letter of each word so long as it is not
    // an article, coordinate conjunction, preposition (etc) unless it is the first word
    // -> traditionally left uppercase if over 4 or 5 letters
    // -> I'm only doing the common ones, add more in the doNotCapitalize array
    if(type === 'title'){
        array		= this.toLowerCase().split(' '); // split on spaces
        capitalized	= '';
        doNotCapitalize	= ["a", "an", "and", "as", "at", "but", "by", "etc", "for", "in", "into", "is", "nor", "of", "off", "on", "onto", "or", "so", "the", "to", "unto", "via"];

        $.each(array, function( index, value ) {
            // only capitalize if first word or not in doNotCapitalize array
            if( index === 0 || $.inArray(value, doNotCapitalize) === -1 ) // inArray returns -1 for false, 0 for element index in array
                capitalized += value.charAt(0).toUpperCase() + value.slice(1);
            else
                capitalized += value;

            if( array.length != (index+1) )
                capitalized += ' '; // add a space if not end of array
        });
        return capitalized;
    }

    // else just capitalize first letter of first word
    return this.charAt(0).toUpperCase() + this.slice(1);
};
 
// Usage:
test = "and this is a test string.";
test.capitalize();		// result: And this is a test string.
test.capitalize('title');	// result: And This is a Test String.
test.capitalize('all');		// result: And This Is A Test String.

Forked and did two things: used the var keyword, not doing so is a personal pet peeve, and used "toLowerCase()" in the 'title' type, which allows for CAPITALIZED SENTENCES LIKE THIS to be formatted properly as Capitalized Sentences Like This, a requirement for a project I am working on.