Anno’s Mysterious Multiplying Jar is a picture book about fractals that my son loved.
Mathematics: From the Birth of Numbers. It got too hard after that, but the historical discussion of how numeracy started at the beginning was fascinating.
A pretty good logic grid puzzle book to check out: “Puzzle Baron’s Logic Puzzles”
Mastermind. We got a book about teaching logic using Mastermind, and it was a lot of fun. Here it is:
Joy of Math
Origami is great. Music theory is now, at 15, quite engrossing. Don’t overlook various kinds of abstract and modern art.
ViHart and her videos and blog to the list. We have dozens of hexaflexagons of different varieties floating around the house at any given time.
We also like the resources from CEMC (University of Waterloo Math Dept.) which can be found here: http://www.cemc.uwaterloo.ca/ If you click on the tab that says “face to face workshops” you can access the math circles materials from previous sessions that cover enrichment topics including some of the ones you mentioned.
We looked at Escher and also fractals/chaos theory too, which are a couple of many great ways to combine math and art.
Also, books by Martin Gardner hold some appeal for my guys, although some get a little wordy at times.
Also, my almost 6 yr. old son is quite visual-spatial, and loves all types of mazes and puzzles, etc. We have a go-to book with a wide variety of fun, thinky, colorful and clever puzzles for the, “There’s nothing to dooooo!” moments. It’s called, “The Brainiest Insaniest Ultimate Puzzle Book!” We love it. http://www.amazon.com/Brainiest-Insaniest-Ultimate-Puzzle-Book/dp/0761143866/ref=sr_1_1?ie=UTF8&qid=1356629553&sr=8-1&keywords=Brainiest+Insaniest+ultimate+puzzle+book
We have another really good one called, “The Big Book of Brain Games,” which has a great range of tons of thinky puzzles, ranging from “Oh, that’s easy!” to “No one has ever solved it.”