I don't have any book recommendations for mandalas, but look forward to seeing some. On other fronts:
The Easy Kaleidoscope Stained Glass Coloring Book is pretty. It's set up so once the page is colored you can post it in the window for a stained glass look. DS and I noticed that the paper wasn't really set for our markers. (It took a looooong time to dry and smeared easily until then. It might have been the easy-clean up kids' markers, though. IDK ) Colored pencils worked much better, but weren't as vibrant on the window. We didn't think of trying crayons. Now that I do, though, it would have been more vibrant than the colored pencils. There was also one with Art Nouveau stained glass windows.
Then there's Ruth Heller's Geometrics. Another one that I want is the Secret Garden coloring book by Basford.