How much time are you planning on traveling? 2 weeks, 4 weeks, 6 weeks? Germany is a BIG country. It will be hard to give you advice without knowing what you are interested in and what your time frame is.

Just to name a few areas:
History/Museums - Berlin
Natural scenery- Bavarian Alps, Black Forest
Castles - Rhine valley, Ludwig's castles
Wine-tasting - Mosel valley

It will be easier for people to give you suggestions if you have some kind of idea of what you want to see in Germany.