Bamberg, an absolute gem of a small city just a bit north of Nuernberg, has a very nice traditional Christmas Market. I think it ends on Dec. 23. The city is also known for the many nativity scenes that are set up each Christmas season. As a bonus, it has one of the best preserved Altstadts you'll find anywhere.

The Bamberg suggestion is a good one. It's such a pretty place and unlike Nburg, wasn't bombed in WW II, so the town didn't have to be reconstructed afterwards. Take the train...it's a nice ride. While you're in town, you can try their famous rauchbier (smoked beer, not to my taste at all, but it has plenty of fans).
Aachen and Cologne are much too far for a day trip, and with all due respect to nukesafe's son, I found the Aachen market to be the most disappointing of all the German Christmas markets we've ever been to. Our favorite was in Muenster, but like Aachen, it's too far for a day trip.

Thanks to all of you for your input. So far I am leaning toward renting a car from Munich, driving to N'burg then back to Regansburg and possibly Passau. Severl of you mentioned Munich's Marienplatz Christmas Market and the crib market a block away. Those are great and I am sure wem will spend time there. I understand there is also a market somewhere in Schwabing and perhaps others in Munich.