Well, aside from FontShop in Kreuzberg, there aren't any foundries left in Berlin, although the city is awash in type designers!

In terms of letters, I love to visit the city's many cemeteries. Here are a few photos – http://www.flickr.com/photos/typeoff/sets/72157600961533746/

The Bode Museum on the Museumsinsel has lots of letters in its basement medieval collection, and also in its large coin collection. The Bauhaus-Archiv might have lettering, but I've not been inside it. There are a number of Soviet and East German memorials with expressionistic stone-carved letters, too. If you go up to the top of the Reichstag, and look down into one of the courtyards, you can see a large lettered installation by Hans Haake.

Near the Rosa-Luxemburg-Platz there are a series of Rosa Luxemburg quotes set as inlaid metal letters into the pavement.

Right now, you can visit an interesting exhibition of graphic design tag-team Ott + Stein, whose works (posters, typographic logos, books) were quite formative and influential for the Berlin scene in the last 3 decades.

Ott + Stein Grafikdesign
The graphic works of Nicolaus Ott and Bernard Stein
Retrospective exhibition at Kulturforum Potsdamer Platz, Kunstbibliothek

Matthäikirchplatz 8, S Potsdamer Platz
Until 15 June 2008. Tue–Fri 10–18 h, Sat/Sun 11–18 h