Links that I use a lot –

3D printing:
http://reprap.org
http://alfa-tech3d.com/
http://reprap.me
http://3dnielsen.com
http://smoothieware.org

General electronics
http://arduinotech.dk
http://let-elektronik.dk
http://elecrow.com
http://sparkfun.com

PCB manufacturing:
http://oshpark.com
http://seeedstudio.com
http://elecrow.com
http://geeetech.com

Software – 3D modeling:
http://sketchup.com
http://openscad.org

Software – Electronics/PCB Design:
http://kicad-pcb.org
http://fritzing.org
http://cadsoftusa.com

Fun – General hack/nerd/electronics so-on:
http://hackaday.com