Personal web sites:
Simen´s Lego page: it has a scanner design (the first expert contest winner) and a proximity detector among other things...
Directional Transmission : it contains pictures and explaination about a directional transmission that allows you to make two movements with only one motor (really cool)
Technica Registry: A register of Lego Technic parts! It has pictures, descriptions and serial numbers...
Jin Sato: This site is in japanese, but you may look at the incredible inventions; there are some videos of two and six legged ambulators.
Joe´s Mindstorms Gallery: other japanese page; it seems that they know what they are doing...
Mindstorms RCX sensor input page: this site has lots of info on the official sensors and how to make your own homebrew sensors...
Robs Robot Page
Artificial Intelligence and Machine Learning > More Outputs: Several kind of transmissions.
Guide to Lego Clocks: Different designs of Lego-made clocks
Killough's Mobile Robot Platform: This page contains a video of a Killough´s platform (omni-directional-rotational traction device)
Small Killough Platform built with Lego: This page contains instructions to build a really small Killough's platform
RCX and Palm: Info on controlling the RCX with your Palm
Lego On My Mind: Very interesting site with many ideas and thoughts
Webrings and "official" web sites:
Lego Mindstorms official web site
Lego Mindstorm´s Webring
Lego Webring (general stuff)
LDraw and similar progs´s Webring
Lugnet News: newsgroup about Lego
BrickShelf: Catalogs and scanned manuals