If you could use a great big free handbook of discrete math and algorithms, Jörg Arndt's fxtbook wants to be your friend. Plain text table of contents to whet your appetite.
posted on Mar 5, 2008 - View this thread

Lightning calculator and "mathemagician" Art Benjamin goes through his paces in a 15 minute video.
posted on Dec 19, 2007 - View this thread

Nowhere-neat tilings are actually pretty neat. We all know you can't "square the circle", but do you know the story of squaring the square? (And by the way, even if you can't construct π with a ruler and compass, you can come awfully close without too much work.)
posted on Dec 4, 2007 - View this thread

Symmetry. Shakespeare. Islamic medicine. Creative writing challenges. Four podcast series from University of Warwick.
posted on Nov 18, 2007 - View this thread

The Prime Game is not really much of a game, but it is a neat & little-known fact about the decimal representation of prime numbers.
posted on Jul 10, 2007 - View this thread

Here are some beautifully rendered views of polytopes, and a few more. The rendering program, Jenn 3D, is free and downloadable, (OS X, Linux, Win) and includes some really dazzling fly-about and camera effects as well as tons of high-dimensional models to explore. There's also a mind-boggling possibility of playing Go on boards in projective space. Via the Math Paint blog, which leads to other interesting places...
posted on Jun 2, 2007 - View this thread

SlitherLink - a little spatial-numerical puzzle. Here's a better exposition of the rules from the puzzle's inventors, and another collection of puzzles. Oh, and a little survey of other sneaky, snaky puzzles.
posted on May 31, 2007 - View this thread

Bending a soccer ball - mathematically. Found via Ivars Peterson's short exposition on Braungardt and Kotschick's The Classification of Football Patterns [pdf, technical].
posted on Aug 17, 2006 - View this thread

Sphere and circle arrangements, the Droste effect, and more: mathematical imagery by Jos Leys. The Droste effect article is informative, too.
posted on Jun 29, 2006 - View this thread

The Sarong Theorem Archive is the premier online repository for pictures of mathematicans in sarongs proving theorems.
posted on Feb 28, 2006 - View this thread

Project Euler is a running contest of programming challenges to hone your algorithm skills. "Each problem is designed according to a 'one-minute rule', which means that although it may take several hours to design a successful algorithm with more difficult problems, an efficient implementation will allow a solution to be obtained on a modestly powered computer in less than one minute."
posted on Aug 20, 2005 - View this thread

The Spidron is an interesting geometric construction that seems to lend itself to folding, dissection, and space-filling in two and three dimensions.
posted on Jul 17, 2005 - View this thread

Michael Hutchings' rope trick and Dylan Thurston's two-handed knot-drawing sk1llz. Did you need to kill some time practicing pointless skills today?
posted on May 6, 2005 - View this thread

The universe in just two symbols. The rest, as they say, is details. No wonder the "Physics Establishment" is trying to keep this quiet. The author, having conquered the universe in general, tackles poetry, as well.
posted on Dec 8, 2004 - View this thread

Minimal surfaces in 3D (red/green, or stereo pairs), with rotate and zoom. If you want to go beyond the eye-candy aspect, here's the obligatory Mathworld link, the classic intuitive explanation, and a raft of additional information. If you like eye-candy, don't miss the ray-traced minimal surfaces and these interesting, but non-minimal surfaces.
posted on Dec 5, 2004 - View this thread