Elder Scrolls Oblivion remains at the top of my single person favorites.
Still playing Everquest II one night a week online with my buddies. It's very much like Elder Scrolls except with other real people running their avatars around. I have also found it great to keep in touch with a couple of old friends. If it wasn't for us all playing MMPORPGs for the last 15 years and now using voice chat with Skype added in instead of text, I'm sure we would have slowly grown further apart but we stay connected weekly, albeit through an alternate reality.
