The brewery is really nice. Definitely worth a stop.
Other New Glarus beers I like. With your timing some may or may not still be around or have just come out:
Fat Squirrel (probably won't be out yet)
Staghorn (oktoberfest, might be out)
Totally Naked
Bubbler
Moon Man
Kid Kolsch
Dancing Man Wheat
I don't really like fruited beers, but theirs are rated very highly. Their Thumbprint series beers are usually really good too. And there are experimental beers you can only get at the brewery. They'll be in the shop downstairs.
For non-NG...Central Waters makes really solid beer, especially their BA stouts. I'm also a big fan of One Barrel Brewing. Wisconsin Amber from Capital brewing is a mainstay when we are up there. 3 Sheeps has some good stuff, but if you find The Wolf, that is the prize.
If you get to madison Young Blood and Karben4, Ale Asylum are solid, but can't remember how much they distribute.
If you see anything from Rhinelander Brewing, avoid it at all cost. Their beers are terrible. All of them. Seriously. I'm not sure how they stay in business. Probably because there's not much in Rhinelander.
I'm leaving a bunch off, including some good ones, but you are going for a race, not to put on 20 lbs.