I've played quite a few.
-Runescape is just rediculous...I can't stand click walk crap.
-WoW is WoW...However I'm on hiatus until the next expansion, although now that I'm away from it...my addiction is dead...which is probably a good way for it to stay...o.o
-Mabinogi...What an awesome free game! I HIGHLY recommend it to people on a budget...it's gorgeous and has an anime feel to it.
-Endless Online ... Only tinkered...it was okay for free...had cute anime sprites...combat system stunk...
-Maple Story...again, a fun free mmorpg with cute anime theme...not my favorite though...
-Furcadia ... purely RPing...no combat or real action...can get kind of lame if your not really a regular there @.@ ...avoid it >.>
-Diablo...you can count it...Awesome game...stoked for III
-FFXI...was a good looking game...the price just didn't compare to WoW in my opinion though...I am a FF lover...I just played WoW first, so the combat system was a major loss for me @.@
Aika Online - Amazing MMO for FREE! Highly highly highly recommend it. The best Free MMO I've ever played...plus lots of us here at the fan play it...so go get it!

...That's all I can think of at the moment...I'm sure there are more...It is a bad addiction that I've been able to sort of break free from as of late...which is always nice ^-^