Okay, here is a list of my all time favorite MMOs, post your oppinions and your own favorites.
1. Lineage 2 (Pay for play)
2. Eve (Pay for play)
3. Silkroad online (Free with an item mall)
4. Rappelz (Free with an item mall)
5. Shaiya (Free with an item mall)
6. Two Moons (Free with item mall)
7. Rakion (Free with item mall, it is a different type of game then the regular mmo I recommend yout try it out. lots of fun)
8. WoW (Everyone knows about this one)
9. Archlord (Free with item mall)
10. Americas army (free to play, developed by the US army, a first person shooter.)