Some readers asked for local parts suppliers and I think it’d be good to have a forum thread where readers can share their experiences.
I start with a list of German online shops:
http://www.watterott.com/ (they offer lots of stuff related to the Arduino and they have nearly all parts you need for the book’s projects including the PING sensor, a protoshield, the ethernet shield, and so on)
http://reichelt.de/ (they offer nearly everything related to electronics, that is resistors, LEDs, and so on)
http://elmicro.com/ (this is a German distributor of http://sparkfun.com products).
The biggest problems you’ll probably have with the TMP36 sensor and the PNA4602 IR receiver. You can always order them from the US, but before look for them on eBay and also ask in your local electronics store. I have chosen the sensors carefully, but you won’t find any sensor that is easy to get in every country on this planet.
Hope this helps!