World at War - Play this turn-based game with 22 maps, including Risk's classic map. - http://www.wawgame.com/
Conquer Club - Free multiplayer variation of the board game. Offers player rankings, alternative maps, individual and team games, and a community. - http://www.conquerclub.com
LandGrab - Web-based strategy game with many extra features such as custom maps, teams, leaders and fortresses. - http://landgrab.net/
Warfish - An online, by invitation only Risk based game which uses a dynamically created image for board display. - http://www.warfish.net/
Dominate - Offers moderated gameplay, a ranking system, game documentation, and a discussion forum. [Membership required for some features.] - http://www.dominategame.com/
Global Combat - A variant where turns are taken simultaneously. Offers a player manual, rankings, and online gameplay. - http://www.globalcombat.com/
CleverMedia: World Conquest - A Shockwave version of a classic strategy game. - http://clevermedia.com/game.cgi?worldconquest