sauerbruch hutton did the gsw building, i believe they are in berlin

barkow leibinger
studio aisslinger
Graft Lab

Henn Architekten - http://www.henn.com

Henn Architeckten Studio B - http://www.studio-b.org

ouf, I had the same problem a while ago. loved berlin as a city but it's pretty hard to find interesting firms there (which is so strange considering how progressive the art, music, etc. scenes are there, and considering how much development is going on...). 

i'll echo barkow leibinger (which has some very cool stuff), sauerbruch hutton (meh), and graft (very cool and theory-conscious but i heard their office is kinda dead).

I'll add AFF Architekten (http://www.aff-architekten.com) which is pretty cool too. 

So funny you say that. When we decided to move to Berlin we were struck with the same conundrum. My boyfriend works for Nieto Sobejano, but it hardly counts as a "Berlin" firm. 

I work in the same building as Sauerbruch / Hutton and they just laid off a buncha people. Recently my boyfriend sent out some resumes and portfolios just to test the waters and got absolutely nada back. Oh well. Everything else is awesome so if our jobs are a bit boring I guess it's okay. 

no one mentions J.Mayer? 

here are some berlin firms and their work (on the right side where it says "Suche nach Bundesland" select Berlin and press "suche":

http://www.german-architects.com/de/buero-profile/architekten-neu-aktualisiert

job board for berlin:

http://www.baunetz.de/stellenmarkt/index.html?s_text=berlin

you can also try http://www.competitionline.com/en/

you could also check out the firms section at architizer.com under berlin

http://www.architizer.com/en_us/firms/?search%5Ball%5D=&search%5Bextended_option%5D=1&search%5Bfi_land%5D=de&search%5Bfi_state%5D=&search%5Bfi_zip%5D=&search%5Bfi_city%5D=berlin&search%5Bfi_type%5D=&search%5Bfi_projects_from%5D=&search%5Bfi_projects_to%5D=&search%5Bfi_employees_from%5D=&search%5Bfi_employees_to%5D=

Here is another website about architecture offices in Germany.

http://www.german-architects.com/profiles/search_results/searchProfiles:1