Here's a great little slide-show with short descriptions of Hofbräu, Schottenhamel, Käfer's, Ochsenbraterei and other tents:
It's the getting in that counts (article in English from www.sueddeutsche.de).

This year the band in the Löwenbräu-Festhalle have written a special “smokers polka” due to the impending smoking ban which will be enforced in the coming year in all German beer tents but is still being challenged.
Never seen the Sueddeutsche carry an article in English on the front page of their website - is this a first?