I'm aware of phpjs.org, but I made a better number_format with better functionalities : I added a 'strip' parameter to say if you want non significant 0 to be striped (9,100 = 9,1), and I changed default values to make them like I want them

better_number_format.js

/* inspired by 
http://phpjs.org/functions/number_format/
http://stackoverflow.com/questions/5731193/how-to-format-numbers-using-javascript
http://stackoverflow.com/questions/7312468/javascript-round-to-a-number-of-decimal-places-but-strip-extra-zeros
*/

function better_number_format(number, decimals, dec_point, thousands_sep, strip)
{
	// default values
	decimals = (typeof decimals === "undefined") ? 1 : decimals;
	dec_point = (typeof dec_point === "undefined") ? '.' : dec_point;
	/* I use a no-break-space character as default thousands separator http://www.fileformat.info/info/unicode/char/00a0/index.htm */
	thousands_sep = (typeof thousands_sep === "undefined") ? ' ' : thousands_sep;
	strip = (typeof strip === "undefined") ? 1 : strip;

	// let's go
	number = (number).toFixed(decimals);
	number = strip ? parseFloat(number): number;
	nStr = number+'';
	x = nStr.split('.');
	x1 = x[0];
	x2 = x.length > 1 ? dec_point + x[1] : '';
	var rgx = /(\d+)(\d{3})/;
	while (rgx.test(x1)) {
		x1 = x1.replace(rgx, '$1' + thousands_sep + '$2');
	}
	return x1 + x2;
}