Uh, Angel was in fact cancelled. A shame too, since now we don't really have anything decent in the tongue-in-cheek-heroes-fighting-monsters genre. Xena, Hercules, Buffy, and now Angel... alas.
Anyway, I agree with a lot of what's been listed so far-- Futurama, Duckman, Zim, The Tick (animated), Brisco County Jr., etc. Great stuff. Now for some more obscure ones. Most of these fall in the "ahead of their time" category.
1. Max Headroom. Alas, too geeky and dystopian for American audiences.
1. Doctor Doctor. A proto-Scrubs starring Matt Frewer (see above).
2. FM. A proto-Newsradio starring Robert Hays (Airplane!).
3.
Quark. The adventures of the crew of a space garbage scow. Sci-fi spoofery a full decade before Red Dwarf hit the airwaves.
4. Police Squad. Sad that so many people don't even realize the movies were based on this short-lived series.
5. Get a Life! Starred Chris Elliot. Too surreal to live. The only series you'll see where the star encounters an ET-like alien, accidentally kills him, and eats him.
6. Liquid Television. MTV's last
good animation show. Well, that and...
7. Daria. This is how highschool would have been for me if I'd been female. At least this series got a proper sendoff. Its cancellation officially ended any reason for me to ever tune in to MTV.