Mannheim or near it
http://www.dessert-werkstatt.de/kontakt.html
http://www.alb-torten.de/
We have a Germanspeaking forum www.torten-talk.de, a few of us also speak and understand English. Joining doesn't cost anything. Diane who founded the forum is English and I am an administrator over there
There will be a new cake competition in Cologne next year in April, check it out. If you need help with the language, let me know and I'll translate the most important bits and pieces for you. The competition is held near the Tolle Torten shop, so it would be a two for one trip. I'll fly over for that as well
http://www.cake-cologne.com/wettbewerb-competition/kategorien/
Another shop I forgot to mention is www.torten-kram.de