Links: DIY Synth and Eurorack Forums
Muff Wiggler: The infamous forum dedicated to modular synthesizers, Eurorack and other musical gear. Hosts a number of official forums for various synthesizer manufactures.
MUFF WIGGLER - Index page
Electro-Music: A classic forum covering the wide-swath of topics in the electronic music world. Contains a special section dedicated to DIY musical hardware and software.
electro-music.com :: Index - electro-music.com
FreeStompboxes: Stompbox is a generic name for any of a group of processors that sit on the floor and are switched on and off using a footswitch. Generally, these are built tough using metal chassis to hold up to the beating they take on the floor.