If MMOs count, try Dungeons and Dragons Online (DDO), it's free to play and you can go very far on free content (don't waste the points you earn, you'll want to buy new Adventure Packs with them).
Otherwise, I'll say Torchlight 2 when it comes out should be pretty easy on the lighter difficulties, and this one will have co-op play.
Until that comes out you could play Titan Quest, but it can get pretty hard in some areas. It's also an action RPG.
You might be interested in Geezer Gamers,
http://www.geezergamers.com/ you should be able to find a group there playing pretty much whatever game just for fun.
Aim towards co-op games rather than competitive, this is where people are happy to carry you a bit.
MW2 is pretty much known as the worst community even among FPS games. My buddy plays a lot of Bad Company (2 or whatever it is), I know he's not outstanding but still manages to have fun.
A smaller FPS that you might like, if you must have one, is Monday Night Combat (MNC), try and find a friendly group that won't throw an epic fit if you screw up while you're learning.