If you didn´t get enough beer and really are into this “old middle-age architecture”-nostalgia-thing:

http://www.andechs.de/

It´s an old (still active) cloister with one of the finest and oldest breweries (since 1455).
You´ll find one of the best german beers (which also means worldwide), if you “dare” also special “strong” beer with 8-9% alc., also about 200 japanese ppl with cameras in 3-4 bus-loads (compared to neuschwanstein: 20 bus-loads japanese), a very pitoresque building and maybe some monks with big bellies.

If you like you also can take part in a guided brewery-tour.

hiten´s analysis is correct - schottenhamel (it´s one m : http://www.festzelt.schottenhamel.de) is one of the most popular. Btw. don´t get wrong in sizes: “Big” means 12.000 drunk people / “small” means 4.000 drunk people per tent. That´s an awful long line in front of toilettes when you need to get rid off yellow juice the most.
Most of the Australian folks are also “Schottenhamel-based”.

The “Käfer”-Tent is kind of celebrity-tent (Paris Hilton was there). It´s pretty difficult to get in there…they often drink more champagne then beer inside - not worth it.

Some advice for the “ritual” to get in there. Normally it´s fully booked, whatever can be reserved and not much pppl without reservation will get inside from 4pm.

Anyone booked gets a secret “password” to reenter whenever they like…After 3l beer it might get difficult to remember the pw…so better write it down somewhere :-)

For the choice Dachau, Neuschwanstein or elsewhere:

Noone needs to see Neuschwanstein …it´s ridiculous time-sink (3h in-line waiting, looking over sheer masses of small Japanese, getting pushed through the castle, that looks like Disneyland…actually noone can say which one was there first :p)

Dachau is best described as Greg said: “powerful human experience”. It could be pretty hard the day after you completeley passed out…and remember my words: you will pass out on Oktoberfest.

The “Starnberger See” could be somewhat relaxing. One Idea to visit (cause Starnberger See is not always accesible, beacause of big estates at the shore from some rich folks):
http://www.buchheimmuseum.de/
It´s a little museum with a very mixed collection, not boring at all, and really nice situated and my cousin actually build the house as an architect :-)

The museum shows the private collection of G.Buchheim - most famous as an author from the book “Das Boot” - the WWII Submarine drama (http://imdb.com/title/tt0081834/ - the ´81 movie) - he was a weird guy.

After all - hope you´ll enjoy your trip, and won´t get lost beanth a bench in a big tent :-)

I assume you’ve watched Beerfest?