U-Bahn and S-Bahn by sswagner
Munich has an excellent public transportation system. These trains cover the city center and serve some places near the city as well. The fare depends on how many zones you travel between. It is possible to get day tickets and a "partner" ticket which can be used for you and another person. This service runs between the airport and the city, so you have a relatively inexpensive way to travel. We also used the train to go to Erding, which has some hotels near the airport if you are flying out early. Dachau is another stop many people take for a day trip from Munich.
In the city, you have direct access to important stops such as the Hauptbahnhof (main train station), Marienplatz, and Theriesenwiesse, the stop for the Oktoberfest. See the link for maps of the system and fare information.