David's Backgammon game download site: Download and try David's Backgammon for Windows XP and Macintosh (OS X and 8/9).
Gaim Tjat: Chat or play online games, including Backgammon.
GameColony.com: Play online games: backgammon, chess, checkers, gin rummy, cribbage, and dominoes. Daily money tournaments with instant cash prizes.
GameSite 2000 Play Online: Supplies online matches, tournaments and games against computer players with different skills. It has membership and guest options.
ItsYourTurn.com: No downloads, no java, just free turn-based (not live) games with thousands of opponents. Play 30+ games including backgammon. WebTV and set-top box compatible.
Netgammon: Popular online backgammon server.
Playmaker World: Playmaker World is a new site for online backgammon and hopes to offer a variety of classical games.
purebackgammon.com: Play a friend at backgammon online, create and compete in online leagues and view player statistics - for free.
True Moneygames: Play online backgammon for real stakes in a secure and licensed environment.