This question is really stressing me out, we need different genre's or something. But, if I'm forced to pick, I'm gonna go with Lost. It's been consistently awesome for 5 years now and still going strong!
There's just way too many to pick just one. here's a few. Family Guy, Dexter, Battlestar Galactica (new & old), Six Million Dollar Man, Seinfeld, MASH, Jeffersons. damn, the list goes on and on.