The best discussion forum for backgammon in English is the
www.gammonline.com bulletin board. This used to be part of a magazine that came out monthly. If you pay $36 once you get access to all of the back issues, and this is better than any book. The discussion board features regular comments by several of the world's best players, including Neil Kazaross and Kit Woolsey. It's run off of the same server as FIBS.
FIBS is a good place to play. I prefer GamesGrid, as the competition is stronger and there is money play, but I think FIBS is the best free server and I still play there.
I also recommend the online magazine
www.GammonVillage.com and the rec.games.backgammon
archive.
I believe there are some active discussion boards in Danish and Japanese, among other languages, but I usually don't read these. At least some of the time, interesting topics are cross-posted.