Only ones I can give you personal views on are WoW, CoH/CoV, D&D Online and Dark Age of Camelot.
I've played WoW on a friends account, and its not bad, but I spent most of my time soloing. I never really got involved with either PvP or Guilds. The game is certainly nice, but it didn't hook me the way it has a lot of others.
D&D Online: Graphics are lovely. Gameplay is pure D&D3 rules, and therein lies part of the problem. The rules when used with a pen and paper group work because you have a DM who can work around player insanity. In the computer, you have few choices, and no way of thinking outside the box.
I also disliked that it forced me to group in order to do some adventures. Within about 2 days I hit a scenario that I simply could not solo, and that kinda did it for me. Also, having dungeons reset if you are outside them for longer than a certain period of time was extremely frustrating.
DAoC I had heard a lot of good things about, and wanted to like, but unfortunately it never really hooked me either. I found part of the quest system frustrating, because I couldn't find a trainer to allow me to choose an advanced career.
I should point out, both of these were just the free trials.
City of Heroes/Villians I like, and have been playing since beta. I am involved with what I consider good supergroups so that does make a difference. The costume editor has an amazing range of choices, and regular infusions of new content also make this, IMO, one of the better games out there.
I came across an ad for this onehttp://www.metin-2.com/index.php
which looks like it might be fun, but haven't got round to checking it out yet.http://www.mmorpg.com
is probably a good one stop site for you to get an idea of the best stuff thats out there.
I have friends playing both Star Wars and Lord of the Rings Online as well, the latter quite popular with my Planetside outfit.