My interests are pretty varied, but history (from ancient to modern) and architecture are probably what draw me most to a place. Medium-to-big cities tend to be my favorite places.
I've wanted to go to Berlin for years, so I'll definitely be including that. I'm also planning to include the Rhine and Rothenburg. I've been to Munich before, but nowhere else in Germany.
So far, my planning and questions come from reading Rick.
Nurnburg sounds interesting because it could be a fairly convenient overnight stop on the way to Berlin, the Nazi center sounds intriguing (and different from other WWII sites I've seen in France), and the old town also sounds like it could be nice to visit.
Dresden sounds interesting because it also seems like it could be a nice place to stop on the way to Berlin, and because of its architecture.
I don't go out of my way to visit countries I haven't been to before, but I brought up Luxembourg because I noticed that it was relatively close to the Rhine and I don't know much about it. I wouldn't want to waste my time going there just to say I'd been, but if it's a lovely place, then why not? =)
PS-This will all be by train.