Risk Factions, an excellent translation and reimagining of the classic board game, is available now on Steam for $10. The game is already available on XBLA and PSN. For those of you not yet familiar with it, Factions includes a short single-player campaign and the ability to play multiplayer using several variants.
If you're a traditionalist, the classic game is in there, too. However, in time the updated versions will likely grow on you for their faster pacing and deeper strategy.