When browsing through Alain Connes' textbook on Noncommutative Geometry, whose illustrations must have been conceived as true works of love, I was wondering if there is a recognized prize for aesthetically pleasing textbooks in Mathematics (and/or the other sciences.)
For what it's worth, I am also very much impressed by the structural and visually beauty of textbooks by Gilbert Strang, Serge Lang, and David McKay (and I sure hope this is not too "soft" a question for this forum :)
The Leroy P. Steele Prize is awarded for expository mathematical works. I share your appreciation of aesthetic value in math literature (which many authors evidently see as unnecessary).