Recently I've been browsing with great delight a recent

book called Mathematical Puzzles: A Conoisseur's Collection,

by Peter Winkler.

 

These puzzles have been chosen because they're typically much

more interesting than, say, the puzzles in the Monthly.  They're

aimed at people with a math background, but not necessarily an

advanced one.  Some of the solutions are fairly complex, but

almost none require math beyond calculus (and very few

go even that far). 

 

Besides a sections on probability, geometry, games,

combinatorics, etc., there's also a non-mathy fun section on 

geography puzzles, a section of especially tough puzzles, and

finally, a section of easy-to-state unsolved problems.

 

Most math-funners have seen some of these problems before,

but I'd guess at least 2/3 of them were new to me, and well

worth the price ($18 on Amazon (paperback)). 

 

--Dan