Ahira's Hangar

Well...

there is Roger Zelazny's Visual Guide to Castle Amber by Roger Zelazny and Neil Randall, which has lots of nice artwork of the characters, little room diagrams of different parts of the Castle Amber

then there is a huge encyclopedia type of reference called The Complete Amber Sourcebookby Theodore Krulik

We have both of those two books at home, and have referred to them regularly.

Not sure if there are any others out there?

Two of the ones that I've used and enjoyed (mostly from the sheer entertainment factor) are the books for the Amber Diceless RP. Mostly, you get some interesting theories about different characters and different ways those characters are going to be interacting with people. Wujck actually talked with Zelazny when writing the books, so readers can also have a little fun with that. I think I have a few PDF excerpts, if you'd like to see them?

D.W.