Jet Photo at Alexanderplatz is where I have my film processed, it's roughly 3 Euros a roll. If you're willing to pay for it, PixelGrain (also Alexanderplatz) is a pro-lab, they do an amazing job. They also process large format.
Foto Impex and Monochrome are good places to buy film at, I usually order at Maco or Nordfoto though, they have most films in stock.
Georg, I'll give the 6x9-back a try one of those days, I'm interested in how it compares to the Mamiya.
//EDIT: But, Lisa just brought plenty of 4x5 film from Berlin, we're going to use that first. I'll come to Berlin this weekend, by the way, I think. How about meeting up Friday or Saturday night? Is Simon in the country?
martin