WoW, even though I stopped playing over half a year ago. Sometimes I just see Blizzard add things that make me think "Damn I'd love to see that." Also Cataclysm, but I doubt I'll play that, Star Wars: TOR has the highest priority for MMO's.
Also Soul Calibur 4 on the 360, even though I almost always get my ass kicked by my little brother, I still want to keep playing it. A part of me must be saying against me: "If you play against him often enough, you'll learn to beat him, you'll see!"