der DIN-A-ARNE hochqualitätslink
If you fondly remember Martin Gardner's old "Mathematical Games" column, which ran in SCIENTIFIC AMERICAN back when that was still a good magazine, you're likely to like this site. It's full of triangle dissections, polyominoes, odd little equations, pretty graphs, and puzzles to be solved. You could spend a lot of time here. In fact, I just might. [via Weblog V2]