Aside from Firefly, which has been mentioned a bunch already, and Mystery Science Theater 3000 (same), the only shows I've watched that had themes with really memorable lyrics were Animaniacs and its related shows. All pretty good, but the best might have been the one for the only show in the lot that wasn't any good, "Pinky, Elmyra and the Brain", which used the lyrics to take a number of shots at the suits' interference in what had previously been an entertaining series ("It's what the network wants, why bother to complain?" "I deeply resent this!")