I'm a big fan of Art and Craft of Problem Solving by Zeitz. The main downside is that there isn't an official solution manual, so checking your work takes a li

I'm a big fan of Art and Craft of Problem Solving by Zeitz. The main downside is that there isn't an official solution manual, so checking your work takes a little more work. But one of the main upsides is that there isn't an official solution manual, so you actually have to work through the problems. :)