I've never really thought about it by network, but here we go:
NBC: My Name is Earl, The Office, 30 Rock, the occasional episode of Law & Order and SVU
ABC: Scrubs
CBS: only Letterman, but rarely
FOX: 24, the Simpsons, House
Anything else is from random cable channels (especially Monk and Psych, like sullim mentioned). I've always been amazed that CBS gets the most viewers since I can't remember watching a single show on that channel other than Letterman or football over the past 15 years. It looks like I watch more shows from NBC than any of the other networks, more proof to the fact that people in this country have no idea what they're doing.