I love the word game, Scrabble, and recently discovered it online through facebook. Now I have several games going at once and play at my convenience. Sometimes, I take my turn right after my opponent has played; but sometimes, I'm busy and don't get back to my games for days. Doesn't matter. Oh, and you can play with random players you don't necessarily know, if you've worn out all your friends and family!
Scrabble gives you a good mental workout, but it's fun, too.