Dexter (Showtime) - premise execution and flawless lead performance (by Michael C. Hall, who has yet to prove he can be this good on another movie/TV role and yes, I'm including "Six Feet Under") carry this show past some glaring holes (some weak acting by the supporting cast) and misfires (Season 3). Still awesome, and Season 4 has brought the show's mojo back with a vengeance. Season 5 will be hawt!
Battlestar Galactica (Sci-Fi Channel) - ending throws things way up in the air when looking back at earlier seasons, but overall a potent mix of sci-fi setting and socio-political commentary brought to life by the best acting ensemble on TV (screw "Lost"

).
Big Love (HBO) - who knew Mormonism could be as much fun to watch as "The Godfather" crime saga? And who knew Bill Paxton could deliver a credible performance as a patriarch wearing way too many hats (father, prophet, husband, perspective-husband-of-fourth-wife boyfriend, businessman, etc.) while keeping multiple family emergencies from exploding. Throw in strong supporting performances from Tripplehorn, Dean Stanton, Sevigny, etc. and this remains one of pay cable's must underrated but compelling dramas.
Weeds (Showtime) - outrageous-for-the-sake-of-being-outrageous comedies that constantly seek to top themselves could have resulted in comedy death. Jenji Kohan and her troupe of game actors haven't fallen flat on their face yet though, and have earned my attention enough to keep me guessing where Nancy & Co. will end up at the end of their 'crime spree.' Kevin Nealon as Doug remains the funniest supporting character in a comedy since... poof... fooooooreeeeeever man!
The Sopranos (HBO) - coasted on its last few seasons, but damn if there wasn't some quality acting (by everybody... seriously, not a weak acting link in the bunch including Robert Iler's AJ whom we were supposed to hate) and tight scripting (by anal-to-a-fault David Chase) that kept the tension and fear of what was going to happen more fun than what actually happened. This show rewards repeat viewing with so many subtle jokes and homages an encylopedia is needed to keep them all in mind. An instant classic.