Available today from booksellers is J.W. Rinzler's The Making of Star Wars: The Definitive Story Behind the Original Film
. It is available in two editions, a hardcover ($75) and softcover ($35). The hardcover includes 48 pages of bonus material including rare storyboards from Alex Tavoularis and Ivor Beddoes plus George Lucas' first recorded thoughts on the expanded universe. Check out the Jedi Journal entries for them here
. There's also a brief interview
with Rinzler at the Official Site.