I love going to market days, especially when traveling by car. I'm planning on visiting Trier, Wurzburg, Rothenburg, Augsburg, Fussin, Munich (I believe Munich I'd daily), Oberrammagau, and Dinkelsbuhl. How can I find out what day is their market day?
Try google with the search term "Wochenmarkt [city name]"
The larger cities will have several markets in different neighbourhoods.
This website might be helpful as well:
http://www.wochenmarkt-deutschland.de/wissenswertes/wochenmaerkte-von-a-z
Most towns in Germany have websites where you can find this sort of info.
Dinkelsbühl (helps to spell it correctly): www.dinkelsbuehl.de. Look under "Wichtig, Aktuell, & Interessant" (important, current, & interesting), then Märkte (markets). Wochenmärkte: every Wednesday and Saturday, April to September, 7 AM to 1 PM.
In Munich, the outdoor Viktualien Market is open daily except Sundays.
Thank you for all of the helpful responses.