Not sure if any of you guys have heard of this before, but there's this browser-based version of Advance Wars that some guy made.
http://awbw.amarriner.com/
Since it's turn based, you can play by email; do your turn and it'll email the guy you're playing against when it's his turn to play.
I haven't really tried it out yet but it seems to be made rather well. The dude is working on a Fire Emblem by Web, which might be more up my alley, but we'll see. I'd like to at least try out a game with someone.
Anyway, enjoy.