Small Bear Electronics - if you're looking for parts for your effects pedals, chances are you will find them here
 

Tonepad - FX projects and you can buy circuit boards for them
 

General Guitar Gadgets - complete FX projects here
 

Geofex - the 'Guitar Effects Oriented Web Page'
 

hammer.ampage.org - Loads of projects here
 

Build Your Own Clone - excellent site, you can purchase kits here with all the parts necessary to build a vintage pedal replica
 

Mod Your Effects Pedals - a site that offers mods to existing pedals by major manufacturers, for a boutique sound without the high price tag. Includes BOSS, DOD, Jim Dunlop, Digitech etc....