There are a lot of TV theme songs that I like.

CSI: NY ~ <i>Baba O'Reiley</i>
CSI ~ <i>Who Are You</i>
CSI: Miami ~ <i>We Won't Get Fooled Again</i> (Yes, I like The Who)
Smallville ~ <i>Save Me</i>
Charmed ~ <i>How Soon Is Now</i>
Gilmore Girls ~ <i>Where You Lead</i>
Buffy ~ <i>Buffy Theme</i>
Angel ~ <i>Angel</i>

...and many more. I don't know what the greatest would be. I just know what I like.