http://www.morecowbell.dj
This website mixes Cowbell sounds with your song, and it goes to your music in most cases. :)
(And for added satisfaction, it can also add Christopher Walken)
Example Song (Piano Man, Billy Joel - http://www.morecowbell.dj/listen?id=DotObq)
(Almost all music I've done so far is better with Cowbell.. :) )