If you plan to visit the shopping area (called Zeil) in Frankfurt, check out MyZeil since they have a pretty big electronics shop (Saturn, similar to Media Markt) on the top floor :3 There's a ton of other cool stores, including restaurants, but I'd avoid eating there since the prices are kind of high compared to other locations (lots of bankers go for lunch there).
We're in Köln drinking Kölsch tonight. Unfortunately we'll be in Paris by Wednesday. But I have enjoyed everything about Germany during our short visit. Hopefully I'll be back soon and get to buy you a round on behalf of us all!