1. The Matrix Online
2. World of Warcraft
I'm not a fan of what Blizzard has done with WoW lately but it simply is the best MMO ever made.
3. Star Wars Galaxies: An Empire Divided
It's Star Wars! and it has player housing.
4. City of Heroes
It was a nice change of setting and played great.
5. The Lord of the Rings Online: Shadows of Angmar
I can play dust in the wind on my lute... enough said!