A Heads-Up for Puzzlers
I would thrust Winkler's Mathematical Puzzles: A Connoisseur's Collection into the hands of anyone interested in problem solving. His selection of puzzles is superb and especially suited for anyone who (like me) tends to enjoy math most when it has a human element. Contrast this with the relentless march of inscribed-pentagons and diophantine equations that seems to characterize most Olympiad-style problem books--it's a breath of fresh air. Discrete and algorithmic mathematics also tend to figure prominently, another plus.
Of the new crop, I've only seen one before (number 3, the 'suicidal monks' problem, here in a more generalized form), but it's an amusing and worthwhile puzzle, which could serve as a good lead-in to theories of knowledge and meta-knowledge.
Oh, and it seems these 7 are a part of a sequel puzzle-book in the works. Thanks, Peter!