Most of the free games aren't very graphics intensive, if you can play WoW you should be fine with whatever else you choose.
Unfortunately there aren't really any good free MMOs out at the moment.
I used to play a crap ton of free MMOs myself. Pretty much quit all of them.
I can't give you any good recommendations, but I can tell you about a few that I have personally tried and you should definitely avoid:
FlyFF: free to play, pay to win. Cash shop items are pretty much a "necessity" to advance
Scions of Fate: Same deal. Really freakin' hard to upgrade too (worse than FlyFF)
Ragnarok Online: bot fest, super guilds rule the server and you cannot join them, and you cannot compete with them either
Seal Online: What a joke, uninstalled in 5 minutes
Kal Online: Uninstalled in 15 minutes. Gigantic fields of emptiness that I couldn't stand running around in
Allods Online: WoW clone. Slow paced, with lots and lots of running around. The beginning part is awesome but once you make it into the open world, you get bored fast.
Corum: This game makes absolutely no sense. Not worth trying.
Shaiya: Really basic MMO. It's not bad, but for some reason it's just not fun to play. It's hard to explain but you get bored fast.
NeoSteam: So freakin' bad the server closed down. LOL!
2Moons: wtf is this I don't even -
Nowadays I spend my free time playing League of Legends and Path of Exile on my computer (neither of which are MMOs). Either that or some games on my PS3.
I think the only MMO game mentioned in this thread so far that I personally tried myself and didn't think was bad is Dragon Nest. All of my friends quit this game too but if I knew anyone that still played I probably would have continued it. It's a very interactive MMO where you actually need move around and aim to hit stuff in combat, so you don't get bored.
There is a bit of repetitiveness in running the same dungeons, but if you play with other people the runs go pretty quick. The Auction House is in this game is probably the best AH in all the free MMOs I've played. (Rappelz is probably runner up with a decent AH too, but that game has some problems so I wouldn't recommend it.)
Good luck, man. D3 is just around the corner. Maybe you can hold out until then. I realize that's not really an MMO either but it's sure to be a worthwhile time sink!