I live and work relatively close to Frankfurt, go there quite often, but have never found anything good to write to TMC about. One place came close, however: In the main train station across from track 26 (IIRC) there is a small Italian espresso shop and they have a beautiful La Marzocco machine. I had an espresso that was drinkable, made from beans sold by Tchibo (!). The beans were fresh and a single was about 30ml with crema, but the shot was too fast (15 sec) and when I suggested it might be possible to do better I received a look as if I probably had escaped from a padded cell. Still, the place had potential.
I've pretty much given up looking for good espresso in this part of Germany. There are a lot of shops opening up, but they either use big commerce coffee (Lavazza or New York or similar) or they don't train their bartistas or both.
Hmmmm, I think we have a member who lives in Frankfurt, but I don't remember who it is.
I would be delighted to hear if you find something good.