South Park is, bar none, my favorite show of all time. It's offensive, it's modern, and the fact that the very first episode had aliens, an erupting volcano, and a monster that made wicker baskets and had Patrick Duffy for a leg set the tone for the entire series. After that? Everything on That 70's Show up to Eric leaving to teach kids in Africa, and then the show became all about Fez and Kelso. They were good supporting characters, but that was it: supporting characters. Hyde, Red, Kitty, Donna, and Eric were the heart and soul of that show, and when Eric and Donna pretty much bailed to go do movies, the show was never the same.
I'll always have a soft-spot for Boy Meets World. I watched it from episode one right up until Corey and Topanga got married. Titus was brilliant, too. It's just a shame that his stand-up is the same exact thing as the show, and nothing more. The Drew Carey Show was a favorite right up until Drew was committed to an asylum after Mimi pulled another massive prank on him (I'm almost positive it was after she sent him to China). Big Bang Theory and How I Met Your Mother are modern faves.