Great inside tip on cheap train tickets in this otherwise expensive country:

Schones Wocheneude Ticket (all of Germany) - 28 Euros (slow trains only, and only on weekends) includes use of all public transit. The coolest thing is that this ticket is valid for up to FIVE people!! So get some other people to chip in a euro here and there, and that's ONE CHEAP RIDE!

Baden-Wurttemberg Ticket (regional by state) - 21 Euros (slow trains only, weekdays) for all same services - public transit, and up to 5 people!