Ever, The Simpsons. But I've lost touch with it the last few seasons.
Recently, I love Game of Thrones, in the I watched season one then compulsively read all the books over a month right after it kind of way.
I got really into Mad Men this past summer and can't wait for the new season in a couple weeks.
And right now I'm really really digging The Americans, which I'm surprised there's no thread on.