This is a simple Music Video Search tool I built with Yahoo! BOSS and YouTube. All you need to do is type in a band or song name and it will start playing the first music video it finds.
Sometimes when I'm really bored, I also just start typing in random words to see what comes up. A few of my favorites are Banana, Pizza and Science.
I have also written an AppleScript that will find a music video based on the currently playing or selected track.
You can download it here: http://gist.github.com/75457. I've set it up so that the file can be triggered by Quicksilver, which is pretty straight forward.
Of course, this was all done very quickly. If you have suggestions or want to expand on it, by all means please do. :)