I've only recently starting picking up some of these, and I've had mixed reviews. I'm looking to pick up a few more, so I'm interested to hear what you guys like.
Art of Star Wars: Episode III - Amazingly good. I loved the layout, and the blurbs that accompanied an image almost always had a really great anecdote describing how it came about. Its always great to hear what was going through an artist's head while he was designing something. The art is shown by the dates it was assigned - before there was even a script in some parts - so you get a cool look at the movie itself evolving as Lucas tries to figure out what the fuck he's doing.
Art of Star Wars: Episode II - Bear in mind I bought this one AFTER the Episode III art book, so my expectations were very high. Unlike the Ep. III art book, this one had the art listed in chronology with the FILM - scene by scene - rather than when by when it was assigned/completed. The blurbs were disappointing, and rather than have the blurbs directly over/under the image in question, they were numbered - then you had to go find the impossibly tiny number hidden somewhere on the picture itself. Drove me insane. The art itself is brilliant, of course.
Boris Vallejo and Julie Bell Sketchbook - Decent, though the descriptions of the images were amazingly skimpy. It sometimes felt like a Dick and Jane book written by Bizarro. "Julie and Boris draw unicorn art picture. They am good at art. They heart art!"