Well, the problem seems to be that there are, at any given, 4 or 5 good sitcoms on the air (not counting animated sitcoms, that is).
80-100% of them are usually on NBC, and this has not changed.
The good sitcoms on TV right now are, in order
1st: 30 Rock, NBC
1st (tie): Scrubs, ABC
3rd: It's Always Sunny in Philadelphia, FX
Normally, the fourth place show would be placed here, but to rank it fourth would indicate it is only one spot below the show above it and only three spots below those first two shows, which I find wildly inaccurate, so the next show will be ranked 8th.
8th: The Office, NBC
9th: My Name is Earl, NBC
Perhaps I am just forgetting something good, so somebody feel free to remind me and/or inform me of any decent sitcoms left on tv after that point