Lighter.js - Demo 

// Hello World in JavaScript
document.write('Hello World');

JavaScript with standard coloring.

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
	"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<!-- Hello World in XHTML -->
<html xmlns="http://www.w3.org/1999/xhtml">
	<head>
		<title>
			Hello World!
		</title>
	</head>
	<body>
		<p>
			Hello World!
		</p>
	</body>
</html>

HTML with Tutti theme.

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
	"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<!-- Hello World in XHTML -->
<html xmlns="http://www.w3.org/1999/xhtml">
	<head>
		<title>
			Hello World!
		</title>
	</head>
	<body>
		<p>
			Hello World!
		</p>
	</body>
</html>

HTML with GitHub theme.

<?php
  // Hello World in PHP
  echo 'Hello World!';
?>

PHP with Coda Panic theme.

/* Hello World in CSS */
body:before {
    content: "Hello World";
}

CSS with Mocha theme.

# Hello World in Ruby
puts "Hello World!"

Ruby with Twilight theme.