Biergardens you say...
Hmm... OK My Favourite large biergardens are (sorry in advance for the spelling):
1) Michaeligarden (near Michaelibad in Ostpark), nice lake setting. Like Seehaus only with less tourists and cheaper prices.
2) Menterschwaige (between Harlaching and Grunwald) high above
Isar banks. Nice atmosphere. I stop here all the time when biking or running. Good food.
3) Alter Wirt (Ramersdorf, near the Chruch). More like a restaurant with a very large outside area(i.e. Beergarden). Very old establishment, and very good duck. The best weisswurst in Munich, but shitty Obadsa.
4) Aumeister...near Studentenstadt. Normal...
5) The Lowenbrau garden on Stiglmaierplatz is decent.
6) Max Emmauel beergarden near Universitat is not big, but it's a nice place none the less.
7) Kugler Alm in Grunwald forest near Deisenhofen/Oberhaching is really good too. And no tourists, but however VERY busy on a nice sunny weekend. Direct on a bike path.