A friend of mine just linked to 20 Science Books Every Scifi Fan (and Writer) Should Read. (By the way, I found his link not on his weblog or via an email but from his del.icio.us bookmarks. If you don't know del.icio.us, check it out: it's a great way of sharing web pages and blog posts that strike you as important — social bookmarking.)
Which science books would be on your 'must read' list? Post suggestions here in the comments and also consider cross-posting to the SPS Book Forum.