I also liked Simmons' book. A bit tiring - it's his typical style from the articles for hundreds of pages, but very well-researched and written. The footnotes alone would make a good book.
Loose Balls (Terry Pluto) is an extraordinary book about the ABA. I'm a fan of books like "A season on the brink" that detail the incidences of an entire season, and within that genre, my favourite is probably The Breaks of the Game, about the Portland Trail Blazers '79 season. That or Wojnarowski's "The Miracle of St. Anthony". One of these two. From recent years, SSOL is probably the best one. It's a shame there's nothing of similar quality about the Celtics 07/08 season. In terms of biographies Foul! The Connie Hawkins Story is easily the best one I've ever read. Recently I've read a very interesting book, "Big Game, Small World". It's an exhaustive but very entertaining and passionate travel around the world of basketball - in more than one sense, as he goes from the origins of the game in Springfield to the playgrounds of Luanda, Angola these days.