The Mathemagician and Pied Puzzler (PDF, rough table of contents here) is a collection of puzzles created by members of the Gathering 4 Gardner Foundation, in tribute to the man himself (previously). Also freely available at the G4G site is Puzzle Craft (PDF), by Stewart Coffin. (The Puzzling World of Polyhedral Dissections, also by Coffin, is available here.)
posted by cog_nate on Oct 1, 2008 - 9 comments

A virtually unlimited supply of randomly-generated logic puzzles, in a variety of sizes and difficulties: Nonograms. Slither Link. Nurikabe. Bridges. Light Up.
posted by Upton O'Good on Nov 28, 2007 - 18 comments

Labor Intensive is a new online puzzle extravaganza in the style of the MIT Mystery Hunt and the aforelinked Puzzle Boat. Appease the Gods by performing twelve puzzly labors. Good luck!
posted by painquale on Sep 22, 2006 - 3 comments

There is an island where all the inhabitants are either knights or knaves. Knights always tell the truth, and knaves always lie [PDF]. Can you tell which is which?
posted by skoosh on Mar 15, 2005 - 18 comments

Arghhhhh!!! Aghhhhhhhh! Arghhhhhhh!!!

Cheats for PuzzleDonkey4 Available here
posted by willnot on Dec 1, 2004 - 55 comments

"WARNING!!! The puzzles on this site are very difficult, and most require the use of a good spreadsheet program in order to solve them. It will take many hours, perhaps days, to solve each puzzle..."
posted by limitedpie on Aug 11, 2004 - 7 comments

A few logic puzzles by Raymond Smullyan . Professor of mathmatics, logic, and philosophy, lifelong magician and concert caliber piano player. Even the titles of his books are fun. Anyone familiar with him?
posted by Mack Twain on Mar 17, 2002 - 7 comments

What Color is My Hat? I [heart] these mathematical conundrums -- simple, easy-to-state, seemingly obvious logic problems that have solutions that completely defy common sense. Here's another you can spring on a friend: "You want to fry up three pieces of french toast. You have a frying pan that is just large enough to accomodate two pieces of bread at a time. If it takes you 30 seconds to fry one side of bread, and each piece of must be fried on both sides, how long will it take you to cook up three pieces (assuming that the act of flipping a piece or adding/ removing it to or from the pan takes no time). Think about it. Answer inside.
posted by Shadowkeeper on May 25, 2001 - 24 comments