links

http://www.solaripedia.com/ lots of case study articles about various solar designs
http://www.builditsolar.com/ lots of DIY solar projects

http://www.robot-italy.com/ (Italy) reseller of Sparkfun, Olimex, Arduino stuff etc. I have ordered from them.
http://www.watterott.com/en/Components/ (Germany) Seems to be nice and cheap.
http://www.robotshop.com/eu/ this shop has large selection and the EU branch ships from France.
http://www.cooking-hacks.com/ Libeliums DIY shop. They design their own stuff too.
http://www.paeae.com/ (Finland) Mainly Arduino stuff, not much to choose from, but located close to where I live.
https://www.m.nu/ (Sweden) Good selection of sensors and 1wire stuff.
http://www.hwkitchen.com/
http://www.active-robots.com/ (UK) good selection of robotics components. I have ordered from them.
http://robosavvy.com/ (UK). Has Dagu stuff in stock. I have ordered from them.
http://www.robot-electronics.co.uk
http://www.technobots.co.uk/
http://robotbirds.com/ anything at the intersection of robotics & flying (UK)
Olimex PCB manufcaturer that produces custom PCBs and is used as a production partner for several open source projects (OpenEEG for example). They design their own stuff too. I have ordered from them.

Sparkfun One of the most well known shops. Designs their own breakout boards and other stuff. I have ordered from them.
Maker shed general DIY. They design some of their own stuff too.
Seedstudio designs a lot of their own stuff. Arduino derivates (seeduino) etc.
Liquidware open source electronics designer. Arduino & Beagleboard shields etc.
Robot marketplace Largest robotics component shop there is. Has lots of non-std. stuff like different kinds of large wheels, motors and controllers for more powerful robots.