At the moment we've a choice of game, listed below as I see it.
- phpDiplomacy, browser-based.
The last few where a good laugh, though the time issues where a pain :/ - NetRisk, browser-based.
I've tried this at home and it seems to run ok, its round robin like the civ games though you can set a time limit on the turns. I've many happy memories of playing this in a pub in monaghan :) - Civ 4
Then there's always good old civ.
I had a look for free pbem games, but they're a bit thin on the ground.
I've stuck a post on the strategy forum on boards.ie so we might get some suggestions there.