Where to start?
Big cities for culture, night life etc: Berlin, Cologne, Munich, Hamburg, Dusseldorf, Stuttgart
Great architecture: Cologne cathedral, Roman sites in Trier, regeneration of Berlin, rebuilt Dresden, Heidelberg castle, Neuschwanstein castle
Scenery: Bavarian Alps, Rhine Gorge, Moselle Valley, Harz mountains, Black Forest, Bodensee, Elbe Gorge, Baltic coast, Neckar valley - these are the big ones, but plenty of scenic river valleys and forests away from the crowds (eg Ahr, Lahn, Weser, Main, Altmuhl)
Pretty towns: Rothenburg an der Tauber (bit of a tourist magnet), Dinkelsbuhl, Nordhausen, Heidelberg, Freiburg, Regensburg, Passau, Lindau, Tubingen, Mainz, towns/villages along Rhine gorge and Moselle valley, anywhere off the beaten track
Food: hope you're a meat eater! Schnitzels are always a good bet.
Beer: goes without saying...
Travelling around: trains are a dream, and not too costly if you take advantage of the various regional passes available (see
www.db.de)
Probably plenty I've missed out, but that's a start!