Cool trip. I think you'll have your hands full cruising Germany/Belgium in a week. I've been to both and there's a bit to see/do. Enjoy driving the Bahn, can be very intense, just make sure to pay attention if you're going to push it. I've done 200 KM/H in an Audi and then get high beamed by both a Porsche and a motorcycle riding my arse. That's intense.

Munich
Skip the Hofbrau Haus. Hard Rock Cafe a la Munich. You can get better beer at smaller places.

Stuttgart/Ulm
Would be cool to visit the Porsche. You're close to Lake Constance which borders Switzerland IIRC. There's a cool castle on the lake.

Rothenburg (http://en.wikipedia.org/wiki/Rothenburg_ob_der_Tauber)
Kindy touristy but what the heck. It's a walled town kinda like fairy tale books. Pretty cool to visit and take pix.

Heidelberg
Cool castle town. I was there for the 800th anniversary, they know how to party...

Frankfurt
So so. I personally like the smaller towns, more character.

Dusselfdorf
FANTASTIC Alt bier. It's also the fashion capital so if you're lucky and there's a fashion show, you're hotel could be full of models. Mine was...

Belgium
GREAT beer. Kinda fruity but I really like the kriek. Fantastic fries, you can't beat real Belgian fries. Found really good waffles too. It's cool (though a bit touristy) to sit in the platz, have a stein of beer, bucket of mussels sitting in butter/wine, basket of fries and just people watch. That was probably the best times I've had in a Euro city.

Den Haag (The Hague)
More closer to Amsterdam but I did drive from Belgium to Amsterdam and stopped in Den Haag. It's a beautiful town, probably one of the nicest I've seen around that area.