There’s a nice Through the Ages play-by-web site at Boardgaming Online. The interface is not very smooth, but it works as long as you know how to play the game.
I’m in couple of games. One of them hasn’t progressed much — four players, different countries — but the other went seven rounds today thanks to local players who all sit by their computers all morning.
I sure would like to play the game on board at some point… It’s one of those games I really like (or think I like, based on what, three plays), but never play.