Rome was excellent (great acting, great dialogue, brought Roman times alive, especially the machinations)
Deadwood - I started swearing more in my everyday life after watching this series but it was absolutely excellent.
Carnivale - mystical, odd, slow-paced but well worth a watch.
Real Time with Bill Maher - slightly puerile, very liberal but I think he's rather funny and has some good showdowns with his panel.

and now for the non-HBO stuff.

American Dad
Family Guy
Scrubs
Father Ted
Futurama
Charlie Brooker's Screen Wipe (for the love of God, please check this out on YouTube if you like TV, he's vitriol, sarcasm and poking-idiocy-with-a-stick right on)

I'm watching Heroes s2 but so far it's so-so, Mohinder and Peter need a big slap, but I've enjoyed the Hiro storyline. Sylar's still king, though!