Dailygammon.com opened last week for backgammon and nackgammon play.
It's free, there are no ads (so far), and it's turn based, so you can
play a few moves whenever you have the time (your opponent doesn't have
to be online). They have ongoing tournaments, but you can also play
non-tournament games. It's better than the other turn based site, It's
Your Turn, because obvious moves are automatically played and because
you can choose from a few different time limits for tournament play.
They maintain a FIBS-type rating system for tournament play. The level
of play for most players seems to be in the intermediate range, but
they also have tournaments for beginners.