All of the pages I discuss here come from one source. I had decided to do puzzles as a topic, but I wasn't quite sure how to research it. I found this site while I was looking for something else (a site on Group Theory). At first glance I didn't think it was too promising, but I dug a bit deeper. If you go to Ed Pegg Jr's Mathpuzzle.com and persevere, you'll find a rich set of links on math, puzzles and related subjects.
The main page is devoted to new additions; recent updates have been heavily oriented toward esoteric geometric puzzles, which is why I didn't think much of the site at first. Unless you're a math aficionado, you might be tempted to skip the main page. Go ahead for now, but skim it eventually; there are some neat things hiding in there, especially in his "My Math Puzzle Pages" section at the bottom (like his page on strategies for combating a superflu and one on fair dice). For now, let's visit his puzzle links section at mathpuzzle.com/Links.html.
I'll skip the URLs for the sites I discuss from this page. Some of them are long and easy to mistype; just visit it, or visit my Brain Candy page (search Google for "Brain Candy" and "catbar" if you don't know where it is); the links will be live there. I think the most addictive puzzle I found from this page is "Paint by Numbers". If you click on the link, you'll get it in English, even though it's a Japanese site. You can get it in Japanese if you really want to. While the concept of these puzzles is simple, the explanation is a bit involved. You have a grid, typically from 10 x 10, to 40 x 40, whose cells have three states: dark, light or neither. Surrounding the grid is information on how many groups of dark cells there are in each row/column and how many dark cells are in each. By deductive reasoning, you can toggle the cells appropriately and reveal the picture. The 10 x 10 starter puzzle is easy, but some of the bigger ones can be tough, as well as tough to read on a small monitor. I was pretty skeptical about how interesting something like this would be at first, but I keep going back. Aak! It just got me again!
Another site I've gone back to a few times is thinks.com. This site has puzzles (especially crosswords and crossword variants), on-line games and demonstrations, images, sounds, postcards, a link to an on-line Spirograph and other items. While there is a lot to do at this site, I was particularly interested in something I found in the "Math Recreations" section called crossfigures. It's like a crossword, but you have to use both arithmetic and deductive reasoning to solve it, given clues like "3 down plus 180" and "A Prime Number". The first puzzle is a bit simpler than the others, with a few easy clues like "Dozen in six gross" and "Five dozen", but later puzzles don't have such generous clues. I've done a couple of the nine they have available. I suspect that the last few will be monsters. Note that some of the links at thinks.com are to commercial ventures and it has some rather visible ads, but don't let that stop you in your hunt for new puzzles.
The mathpuzzle page also has links to WIMS, a French interactive mathematics site, available in English and French. Most of the large number of links here are heavy duty stuff, like solving a jigsaw puzzle using affine transformations over finite fields. For the most part, this is a site devoted to esoteric mathematics, but some of the tasks are in essence, puzzles and games. If you had much math in school, you'll probably find some fun here, for some definitions of "fun".
Here's one more link that you might like from the mathpuzzle site. Go to "Andreas Ehrencrona's Life Applets" to find a really good implementation of a computer simulation called "Life". It's not related to the board game. It's based on a set of rules created by John Conway, which are used to create a simulated environment where various configurations of cells grow, reproduce and die, based on their local conditions. "Life" is an ancient (in computer terms) field of experimentation; I wrote a machine language program for "Life" on a Commodore-64 over sixteen years ago. If what you see here piques your interest, you can find tons of other, more detailed information on the web (Google: "life" + "conway" = 53,000+ hits!), in back issues of Scientific American and even a few books.
I've only scratched the surface of what's in the links section of mathpuzzle.com. There are links to puzzle, cryptography, math, Scrabble and game design FAQs, places that sell puzzles, game sites and a lot of other interesting sites. Puzzle and game fans would do well to comb this site carefully.
See what following just of few of the links from one page can lead to? If I spent the time to be exhaustive on puzzle pages, I could come up with hundreds of great pages. You could waste your entire life on 'em. The biggest puzzle I have is to figure out how I'm going to stop visiting these puzzle sites.
CATBAR - Brain Candy #35 - Puzzling Out the Web / Brian Rock / June 21 2000