Oh, and since everybody is dying to hear my personal canon (read: nobody but me cares what my personal canon is, which is how it should be; I'm just going to tell you because I damn well feel like it), here it is:

A New Hope's novelization (only the unique elements that are not contradicted by the below)

A New Hope (2004 DVD version of the film)

Return of the Jedi (2004 DVD version of the film)

The Phantom Menace (2001 DVD version of the film)

Attack of the Clones (2002 DVD version of the film)

Prologue to Shatterpoint (only available in the paperback version)

Revenge of the Sith (there's essentially only one version of this film)

I also include the 2004 version of The Empire Strikes Back on a provisional basis, as RotJ does make direct references to its events. My reasoning behind this rather odd canon is that everything in the above list with the exception of the ANH novelization was either written solely by GL (ANH, TPM, RotS, Shatterpoint's prologue) or written by Lucas with assistance from others (RotJ, AotC). While GL was the originator of ESB's story, he did not write the actual script. Shatterpoint was written by Matthew Stover, but the prologue added in the paperback version was written by GL himself. The ANH novelization was written by Alan Dean Foster, but GL gave him permission to use his name as a pseudonym, so I threw that in there for the heck of it (also because it was the first SW product ever released). I don't claim this to be official in any way, nor would I argue its merits in a debate. This is just what I think pure, undiluted Star Wars is. It's just my opinion, and I am not so proud as to make it sound like anything more.