Coinciding with Aion's "realistic humor", but different. I find terrible things funny in US TV shows and movies; If there unintentionally funny or borderline - Should I laugh? - Like a extreme car crash, pulled off in a way we're meant to feel emotional for the characters, when it's actually just hilarious. Even the people on the set must be laughing.
The one, the only, the messy and subjective Cartoon Debate: South Park is brilliant, It works episodic, yet each season new characters come and go, jokes are brought up, and the characters grow. It seems like you won't get attached to the show, unless you know it's history. Futurama can be amazing, sentimental and clever, if the writers are up to it with episodes like Space Pilot 3000, One's set in the Year 2000, and the one with Fry's dog... Even Bender's Big Score. [Speaking of which, I need to watch Bender's Game.]
The Simpsons has, without a doubt, lost the plot. Some of my favourite ones, are still funny (The BoyBand episode). Yet, Fox insists it goes on. King of the Hill has it's ups and downs. I haven't seen half as many episodes of that to give a full judgement of it, though. And, finally, Family Guy. I watch it occasionally when it's on, but it grates with me. I knew a kid who consistantly quoted it. And the ability to quote a show is it's downfall (Exception being Invader ZIM. "Random is funny", yeah) ;/
Aqua Teen Hunger Force continues to succeed.