Under "Logic Puzzles", through To Mock a Mockingbird (about to reread it because I read it years ago and a lot of things didn't stick at that point). I picked up his books to flesh out my home library (I'd read some of them back in college) and started rereading from the beginning. Have a notepad and pencil to help puzzle through the problems (or index cards, I have a few stuck in the books).
They span from riddles, to logic puzzles (the classic Knight & Knave puzzles), to computation-based puzzles with combinators.
