We've got some pretty interesting books in our backlist. Here are a few more general interest ones that people might be interested in:
Origami Design Secrets
The Cryptoclub: Using Mathematics to Make and Break Secret Codes
From Zero to Infinity: What Makes Numbers Interesting
Project Origami: Activities for Exploring Mathematics
Mathematical Puzzles
Connection Games
The Mathemagician and Pied Puzzler: A Collection in Tribute to Martin Gardner (and several other similar books)
Puzzles 101
Robots Unlimited
How Noble in Reason