I also play Mabinogi (thanks, Jana), though I haven't had a lot of time to do so this week. Also have some characters on HatRO, and occasionally I'll hop on MapleStory to help my little brother out with some things (though by this point he's probably a higher level than me, if he's been playing regularly).
Furthermore, every so often I'll hop on Runescape to see how it's changed over the years; it was my first MMO, so despite the bad rap it gets, it'll still have a place with me.
Not sure if Estiah and Kingdom of Loathing technically count as MMOs, but those too.