The past few weeknights have been spent solving puzzles from Martin Gardner's books, which I really enjoy. I just came across a book by Peter Winkler, whose name I had heard before in talks by Muthu. After reading a few of the puzzles on Amazon's look inside preview, this book is too hard to resist buying. Also, here [PDF] is a beautiful set of 7 puzzles compiled by Peter Winkler on the occasion of a remembrance for Martin Gardner in 2006. Other places I have found good puzzles recently include this page maintained by Gurmeet Singh Manku. Puzzles + coffee + weekend afternoon = awesomeness.