May I suggest Penrose the Mathematical Cat? There are lots of fun, recreational math ideas in there. Also the "Sir Cumference" series is good.
Cool topics:
Sequences, functions, graphing stuff, fractals, binary/other bases, other number systems, codes, pentominoes, tangrams, money. My mathy DS5 likes to play Descartes' Cove with me. He needs help but he is fascinated by it and learns a lot of math from it. I think of it as a fun teaching tool.
Please post any good stuff you find. I'm always looking for things, too!
