Hop on the first train to Munich!!! j/k I've been to Frankfurt once for a week on business, but really didn't do any touristy type things. Just worked and then went to some really good dinners and then out to the clubs. If you go out at night be cautious of the hookers in the clubs, unless you're into that kind of thing
If you like classic heavy bavarian style food, sausage/meat/potatoes yummy!!, ask for a "biersch(sp?)" style resturant. Drink plenty of wheat beer and let me know when you are heading to Munich. I've spent lots of time there and can give better advice for things to do.