I'm playing on:
Dailygammon - of course (very interesting cause its a completely different way to play BG )
Playok (polish site, many players from eastern europe there, faster play than on fibs, no client needed, matches are recorded, PLAYING WITH TIME LIMIT, official tourneys 5 times a week swiss system, ERVERYBODY CAN START TOURNEYS IN SWISS SYSTEM THERE)
I'm playing occasionally on:
freenet.de (only single games,no rating, score based on differencees of pipcount when you are winning, only german players there)
I stopped playing on:
Gametwist (players refuse to use the cube, weird rating system, people dont understand the cube, VERY RUDE BEHAVIOR)