Recommended stops for trip from Munich to Berlin?

To start with, Dresden and Leipzig.

Many, many years ago, I went in a bus full of college students from just south of Stuttgart to Berlin and back. In those days we had to stick to the corridor as we were driving through the DDR. On the return plans were made for us to stop in Leipzig where we saw St. Thomas church where Bach was, Thomaskantor. We spent the night in a hostel further south. We split up and one group went into Weimar and the group I was with went to Buchenwald. Buchenwald was a camp that had a lot of communists in it as well Jews. The tour was powerful although in those days the emphasis was on the communist prisoners over the Jewish ones. We also went to Wartburg Castle in Eisenach, which is just west of Erfurt. This is the place where Luther hurled the Ink Pot at the Devil. It's a little be more on the way to Stuttgart, but might be worth the side trip. BTW when I took my Rick Steves Berlin, Prague and Vienna trip last year, our guide was from Thuringia. He pointed out to us how very few big towns there are and how rural it is. He grew up doing winter sports and hoped to be in the elite DDR program. Sadly, Christmas cards from a grandmother in the west nixed that plan.

Pam

You might want to put Frankfurt on your list. We have a whole row of wonderful museums and art galleries along our riverbank. For history, you can't beat going to the cathedral where the Holy Roman Emperors were elected and crowned, or visiting the Holocaust Memorial Wall or the last remnant of the Ghetto wall. Or if you like, you can go take a look at one of the only examples of a "hanging vault" that still exist, in our St. Leonard's church which was built in 1200. Even our main train station is a thing of beauty. Hope you decide to visit.

Nuremberg is a great choice. I hope to go there again someday. I would highly recommend a night in Rothenburg ob-der-Tauber. It is a beautiful medieval city, quite tourist friendly, great shopping and Christmas store, and the highlight for me and the people I have taken is the Nightwatchman's tour (evenings at 8 I believe). Everyone loves it.
The Hotel Klosterstuble is good place to stay.

Hope you have a wonderful time.

Adding to the places mentioned by others and focusing, as you requested, on a "relatively straight trip from Munich to Berlin":Starting in Munich and going north:RegensburgBambergWeimarNaumburgWörlitzPotsdam (would be done as a day trip from Berlin)