Coming soon: Classic puzzles
Conceptis Puzzles - Free puzzles, including Sudoku, Slitherlinks, Battleships, Paint by Numbers (they call it Pic-a-Pix), Link-a-Pix and other puzzles. Registration is required, but well worth it. They send a periodical newsletter, but they are in no way irritating.
Solving Slitherlinks - Here I explain a faster way to solve Slitherlink, using the parity method. Learn how to solve these addictive puzzles!
DJAPE - This name is known among all serious sudoku-ers on the web. Djape creates not only regular sudokus, but many variants, including Samurai, Butterfly, Flower, Killer, Odd/Even, Non-consecutive, Consecutive, etc. Recently he's even flirted with Paint by Numbers (he calls them Hanjie). He also created the software "Perfect Sudoku". Check it out. All of his puzzles are good quality.
Brain Bashers - I've recently discovered this site, mainly because of its sudoku resources. They do a good job explaining techniques. This site also features other puzzles such as Paint by Numbers (he calls them Nonograms), Puzzle Loops, and Bridges. If you go there, don't forget to try out their Blank Page.
SudoCue Solving Techniques - This is by far the best sudoku solving website I've come across. Colorful demonstrations help to clarify lots of techniques that are floating around. If you need help, come to this website.
Sudoku Forum - Come to this forum to discuss sudoku puzzles, technique, etc.
Killer Modulo Sudoku - An interesting variant on a variant. These puzzles are just like Killer Sudokus, except only the ones digit is provided (meaning you must determine the tens digit in a cage).
Sudoku History - I first came across a Sudoku in GAMES Magazine years ago. I can't remember what it was called, but now it's known as Sudoku all over the world. Where did it come from? Why has it become so popular? Also, click here to see a sudoku puzzle from 1895.