Some good suggestions in here I'll just chip in on...
Spartacus (Blood & Sand, Gods of the Arena, and soon to come, Vengeance. No need to say anything else.)
Battlestar Galactica (The 2004-2009 series. Fucking epic is all I have to say. I didn't watch it for the longest time and finally caught up with the whole thing on Netflix. Can't believe I never saw it before.)
Dexter (You'll love this one - very original series that'll keep you on the edge of your seat most of the time. And you never know who's gonna die either since they have no problem killing off main characters... no one's safe!)
Homeland (New series that just came out, shows right after Dexter. Didn't expect this one to be the gem that it is. Really awesome series as well. 1st season just ended.)
Generation Kill (Awesome choice. Derived from accounts written by a journalist that was embedded with 1st Marine Recon in Iraq. Read the book and watched the series - both were great.)
Trueblood (definitely more hardcore than Twilight - interesting twist away from the usual Vampire stories, where Vamps are attempting to meld in with the rest of the general public and become accepted into society. At least that's how it starts out and then shit gets really crazy.)
Dollhouse (2 Seasons. Made by the same people that did Firefly. Loved this damn show, wish they had more seasons to it.)
Firefly (Pretty damn good. I think I expected more because I heard so much about it, but it's still great)
...and of course, Band of Brothers and The Pacific.
