MUD Development
Grim Wheel - If it's on the Internet and related to MUD development, you can find it from here.
Programming Sites
Bit Twiddling Hacks - Full of clever bit manipulation algorithms.
Chris Hecker's Website - Chris's writings on game design are very insightful. Not updated very often.
Scientific Software and Graphics Algorithms - Algorithms and papers on filtering, graphics, root finding, many handy topics really.
The Inner Product - This site has many interesting ideas and articles. Sadly, it hasn't been updated recently.