lileks.com: One of the most interesting Web sites out there. A sprawling, complex, witty, funny, and insightful commentary on culture. Includes such gems as the Gallery of Regrettable Food and more.
everything2: This site is an experiment in hyperreality. It's a free-form, collective web of ideas and concepts. Browsing through this site is addictive and intellectually stimulating; you can get lost here for days.
False Advertising: A gallery of parodies of famous brands, ads, and logos. Sometimes vulgar, often dead-on, and very funny.
Movie a Minute: Miss a movie you wanted to see? Get the complete plot in a half-dozen words!
The Complaint Letter Generator: A Web site that automatically generates complaint letters. Key in a person's name or an organization (eg, Microsoft), and the program will rant about your chosen target.
Project EUNUCH: Take an old 486 computer, a freezer, a LOT of alcohol (some of which is used for coolant), and you too can overclock a 486 to 247 MHZ before it melts!
Apple Fritter: Man, Apple fanatics do the damndest things to their computers...
The Register: Excellent site reporting on the news in the computer industry without hype or puffery, and with humor.
The Foresight Institute: Nonprofit research center for nanotechnology. It doesn't get more cutting-edge than this.