Hey there, from starting with some of my random projects, I've built up a nice list of parts suppliers...I figured I'd list'em here for people. Most of these websites have english versions for anyone that isn't a germany resident.

http://conrad.de - random hobby place/electronics supplier

http://watterott.com - stepper motors and a wide range of other supplies, including adafruit shields and mannny pololu products.

http://Fritzing.org - for breadboard protyping and circuit board design
http://reichelt.de - random hobby place/electronics supplier
http://screwsandmore.de - extremely cheap, and high quality stainless steel supplier (I buy exclusively from them)
http://lipoly.de - another hobby store
http://maedler.de - cheap supplier of plastic pullys
http://formulor.de - Ponoko DE outlet
http://tinkersoup.de
https://zahnriemen24.de/ - Cheap DE supplier of Belts (very cheap)

All of them ship international...But of course, it's better if you're in germany 😛

hope it helps.