[Request] A Plugin Which Will Suffix All the URL with something

I have written following code

function wp_external_links($text) {

	$pattern = '/<a (.*?)href="(.*?)\/\/(.*?)"(.*?)>(.*?)<\/a>/';
	$text= preg_replace_callback($pattern,'parse_external_links',$text);

	return $text;
}

It does nothing. Here I am trying to replace all the occurence of <a href= with a prefix.

it worked. Great. But not how I wanted. But still I can work on it now. Thanks for efforts.

If someone can develop this into a real plugin with some admin options please do. Its a nice idea. ??