There are a lot of shows I pick up and put down, so it's actually fewer than I thought. I don't count stuff I watched while it was on the air, just stuff I've plowed through on DVD. I feel like I've seen every single Seinfeld episode, though.
The Shield
Sopranos
Red Dwarf
Buffy The Vampire Slayer
Angel
Babylon 5
Dharma & Greg
Firefly
Ultraviolet
Harvey Birdman Attorney at Law
Andy Richter Controls the Universe
Ghost in the Shell: Standalone Complex (the only anime I ever made it past the first episode!)