DailyGammon, a site purely dedicated to correspondence backgammons, is probably an exotic site to start with, but this is where I’m spending 80% of my backgammon time…

Backgammon Galaxy is the most modern site for playing backgammon online, and it’s the most serious site for serious player – you can’t improve your rating by luck. Only by winning a match and having played better you will improve your rating.

Backgammon Studio Heroes has every feature you can possible think of for an online backgammon site. It’s sometimes a bit confusing, but alone its wonderful “consultation match” is worth the price of admission. Highly recommended.

Lord of the board is not primarily about playing backgammon, it is about getting your money. There are much better sites.