Need rec's on great multiplayer, turn-based, over-the-web iPad games

[chartier]

A friend a couple states away just got his first iPad and we're looking for one or two great multiplayer, turn-based games we can play. We're flexible on the genre and other details of the game as long as can play either with or against each other and take turns at our leisure since we're both pretty busy.

Any ideas will be much appreciated!