I really wish I had a chance to read this topic sooner - this is a tough one. So in no particular order other than they came to mind ...
1. Griffin and Sabine: An Extraordinary Correspondence by Nick Bantock (and the other two as well). These were beautiful books, though some of the artwork was very, um, odd. They chronicle a conversation between London card-designer Griffin Moss and South Pacific islander Sabine Strohem conducted on handmade postcards.
2. Masquerade by Kit Williams is a children’s book, with lavish artwork that concealed clues for a treasure hunt for a jeweled golden hare that was hidden somewhere is Britain. It was really depressing that the person who 'found' the treasure cheated. Sigh. Also that it wasn't actually a puzzle that could reasonably be solved by a child. However the artwork is still masterful.
3. The Plant Hunters by Caroline Fry contains folders with maps of historic gardens and other facsimile documents that you can pull out and handle. Plus the illustrations are gorgeous.
4. I have a facsimile of the Voynich manuscript which is a 15th century (1404–1438) illustrated codex written in a constructed language, code, or perhaps just complete gibberish, that has never been deciphered. Nobody has any idea what it says, or if it actually means anything at all, though it is a pretty elaborate piece of work just to be filled with nonsense.
Lewis Carroll, with commentary by Martin Gardner, is a highly footnoted Alice in Wonderland and Through the Looking Glass that explains some things, gives historical perspective and basically folds a whole 'nother book into the original. It makes for a unique reading experience and gives you lots of things to think about while you read.
6. Hippolyte's Island: An Illustrated Novel by Barbara Hodgson was quite unique. Again, something very lavishly illustrated and with the added bonus that you have no idea of everything is real or an elaborate hallucination. Honestly, I am still not quite sure what I thought of this book. It was sometimes boring and/or frustrating. Then it would get interesting and it was always lovely to look at.
7. Radioactive: Marie & Pierre Curie: A Tale of Love and Fallout by Lauren Redniss is a unique approach to biography. I am reading this one right now and I am still not sure what I think of the artwork. It definitely stands out.
8. The Invention of Hugo Cabret by Brian Selznick- I am sure that most everyone is already familiar with this one but I still like it, as does my son.
9. Still can't make up my mind for this one. How about Flotsam by David Wiesner. Absolutely beautiful and there is no text but it tells a clear and compelling story.
S. by J.J. Abrams and Doug Dorset. It has all that marginalia and tucked in neat stuff. I am looking forward to reading it. (My TBR isn't a pile, it is a mound).