Lucid Technologies has some great, inexpensive EPROM burner kits. All you need is a serial port and a terminal program; these are "smart" devices that do the work themselves without tying up a host computer.
ARRL Hamfest Calendar: Best electronic bargains in the world (get there early--don't forget a flashlight)
Iridium Flares: Impress your friends with your knowledge of lights in the sky (check out the prediction service link)
Silicon Sam: Home of lots of repair FAQ's, the one and only Laser FAQ , and lots of other HV stuff.

Some of these people are slightly insane:

Jochen's High Voltage Page: HV, radioactivity, the Farnsworth/Hirsch Fusor (Hot Fusion!)
The Arcstarter: With a name like that you'd expect... the corn cannon and all sorts of other fun stuff

Synth DIY

Synthesis Technology: MOTM series, CEM chips, tempco resistors
Geofex: Guitar-oreinted effects circuits and projects. Lots of useful info even if you don't play guitar.
Blacet Research: Module kits
PAiA: Still makin' those kits

Mac

XLR8 Your Mac: Tons of Mac upgrading info including daily news page and links (check out the sponsors' specials)
Speed up your CPU at the Clock Chipping Home Page:
Keep up to date (daily) with the latest Mac software, find stuff you didn't even know about

More to come--I'm just getting started