I'm an advanced/expert level player, usually rated from around 1850-1900 on FIBS, currently 1900.

I third the recomendation for Magriel's book. It is still the best overall introduction to quality play. I bought the paperback reissue from Carol Joy Cole. Search google for her website, she's well regarded by backgammon players as a supplier and I know I have had outstanding service.

If you want to play seriously you should look into joining Kit Woolsey's Gammonline website. It's full of terrific articles and has a bulletin board where some of the world's best players post daily. A lifetime subscription was only $35 last I saw. Lifetime since they are no longer updating with new strategy articles (used to be a yearly fee) but it still has all the past articles. And the board itself is so helpful with answering questions and posting interesting positions that it's an unbelievable bargain. The members vote daily for the move in an ongoing match against Woolsey himself who is a well known world class player. Lot's of fun. Going through the archive of past 11 point matches of Woolsey against the readers taught me far more about backgammon then any book ever did. Kit's comments on each move (he comments on every move and cube decision for both himself and the readers) are very clear, and suitable for the full range of players from beginner to world class.

GammonVillage also is very good. I joined and being able to read Walter Trice's 'Backgammon Boot Camp" series of articles was worth the money. In fact, he published the articles as a book by the same name and next to Magriel I think it is the other outstanding book for someone who is new or intermediate but wants to become good.