I would bring back (oh the nostalgia):
Whose Line is it Anyway (I want new episodes please)
Mystery Science Theater 3000 (I can't believe no one has said this yet)
Cheap Seats (one of my favorite shows of all time, on ESPN Classic, no less)
MTV Unplugged (they'd have popular bands do their most popular songs on acoustic, it was really good)
Corner Gas (best sitcom ever, even if it was Canadian)
Deadliest Catch (before the government imposed fishing limits by boat, taking the competition out of it)
Now for some cartoons:
SpongeBob Squarepants (the old stuff, the new stuff is terrible)
Rugrats (possibly the best cartoon ever)
Angry Beavers (possibly the second best cartoon ever)
Hey Arnold (possibly the third best cartoon ever)
CatDog (possibly the fourth best cartoon ever)
Rocket Power (possibly the fifth best cartoon ever)
All That (it was like SNL for kids)
Now for some really old stuff:
Alex Mack (oh my, this one's old)
Doug (this one is also very old, and was the best cartoon of it's time)
Rocko's Modern Life (very, very old, and was the second best cartoon of it's time)
The Adventures of Pete & Pete (freakin' awesome)
Kablam (so old, but so good, one of the first shows made by the people who went on to do spongebob and others)
Man, I'm really remembering some old ones.