Babylon 5 - One of the best shows ever. The plotlines were tight, the surprises were many, and the way everything was woven together was nothing short of incredible. This is a show you can watch over and over and still enjoy how things are built up to climax. The last season was a little weaker, though, due to fears of an early cancellation in season four and a major cast member leaving the show. Still good, but not up to the first four seasons.
Quantum Leap - Scott Bakula is a superb actor. He leapt into several characters, and made them all believable. I mean, you may laugh at him at first in a dress when he's portraying a woman, but you believe it in the end. Add to that some fun shows, nice little nods to history, and a few plot twists that kept you interested, and it's a show well worth your time.
Scrubs - proof the Emmys don't know what the Hell they're doing, that this show hasn't been nominated each and every time for Comedy and Actors and Actresses. You will howl.
Arrested Development - another show that will make you laugh - and you never know where the Hell it's going.
Monty Python's Flying Circus/Fawlty Towers - The pinnacle of comedy.
M*A*S*H - For Alan Alda's Hawkeye alone.
Picket Fences - Again, forget the last season and enjoy the first ones. I have never forgot Rome, Wisconsin. This is the show that David Kelley keeps on trying to recapture and ends up getting wrapped in whimsy.
The Muppet Show/Sesame Street - Hey, I'm a Muppet fan. But the Muppet Show is still funny, and Sesame Street deserves a place of honor for its contribution to children's education.
Gilmore Girls - The wittiest of shows out there now, and you gotta admire the writing that boldly references things from Oscar Wilde to The Girl On the Bus.
Buffy the Vampire Slayer/Angel/Firefly - Any Joss Whedon series is worth checking out. I'd have Angel and Firefly up at first, with Buffy either close behind (first four seasons) or a distant second (last three).
Teen Titans - The best story line new animation I've seen so far.