I'm in an interesting position here. I live in a little Bavarian town about 40 miles SE of Munich (so yes, Oktoberfest every year, not to mention the smaller, much better ones locally). I have a HUGE selection of German/regional/local/VERY local beers at hand, but it's difficult to get any NON-regional beers. You can get a few from Italy/Holland/Britain/etc, but forget about any countries outside Europe.
Still, look at what I have at my disposal? Probably 40 different breweries in the local 30km radius, many of them making a Helles (lager), Weissbier (wheat beer), Hefe-Weissbier (wheat with yeast), Dunkel-Weissbier (dark wheat), Dunkel, Pils, spring brews, fall fest brews, winter brews, etc. All cheap (an average case of 20-.5 liter bottles costs about $12, inlcluding about 3 in deposit, which you get back). So I'm paying about .50-60 cents a bottle for stuff like Paulaner, Spaten, Franziskaner, Hofbrau, etc. Doesn't get much better than that.
Some of my favorite regional beers are made by:
Floetzinger - I think they only make 1 export, a lager. Their 1543 Hefe-Weissbier is a food of the gods.
Ayinger - Many beers exported. Their Celebrator is one of the finest beers EVER.
Franziskaner - The Weissbier 'division' of Spaten. A consistently good wheat beer.
Eine Bayern Halbe - Very regional. They make a wonderfully tasty Helles.
Oettinger - Very nice, well-rounded beers.
Schweinsbrau - They make two beers in Hermannsdorf, an extrememly nutty dark Weissbier and a smooth, unfiltered Helles, each made with wholly organic ingredients.
Unionsbrau - It's a small brewery in a cellar in Munich that makes only a delicious, smooth, creamy, wonderful unfiltered Helles. Very cool place if your a beer fan and in Munich.
Of course, I have scarcely met a beer I didn't like.

Speaking of growlers (called Siphon in German), I have 2-2 liter ones, from Unionsbrau and Airbrau, another great brewery in the Munich airport. They kick ass.