Links

(AKA hoarded bookmarks)

Music/audio

The Conet Project Highly fascinating (and also creepy) recordings of shortwave numbers stations... Soundcloud/Internet Archive/Free Music Archive
Every Noise at Once A gigantic, messy map of musical genres.
Radio Garden Possibly my favorite of all the sites, a sort of world map/radio tuner crossover. Move over the dots to listen to certain regions and stations within those regions.
University of Twente WebSDR From the University of Twente all the way in the Netherlands. This controls a shortwave reciever, allowing you to listen to shortwave radio and all that stuff from the comfort of your very own browser.

Fun/Games

Space Cadet Pinball A fully working in-browser port of the classic Space Cadet Pinball PC game
Minesweeper An in-browser port of the classic Minesweeper game (no bloat!!!)

"Tools" and useful stuff

Oblique Strategies A browser version of Brian Eno and Peter Schmidt's Oblique Strategies card "game," serving as prompts to get through creative block (although I have absolutely no idea how to use these). Wikipedia may explain better than I can.
Story Plot Generator From Big Huge Thesaurus, this is a random story plot generator if you ever need ideas/inspiration for writing. Some of these can get pretty absurd, and are good for a laugh (which is exactly why I like this).