I can't think of anything besides Maui Brewing Co but most of the bars carry at least some local beer.
We went there about a year and a half ago. Great time. Are you planning on going up to Haleakala summit? Definately well worth it if you have the time. Those half-day cruises with snorkel packages thrown in are also fun if you are into that stuff.
Ok, making my way through the line of Kona products, and they are very nice indeed! I'm still flabbergasted by the selection and low price of beer here. 24 SNPA for $25 at Costco. Canada sucks the hind tit when it comes to beer, it turns out - even Hawai'i kicks it's ass, and they have to import everything.
I honeymooned in Maui in Sept. 06, spent one glorious morning watching watching 1:00 football games (which started at 10am Maui time) meanwhile sampling everything Maui Brewing Company had to offer. As far as breweries go its nothing too special, however I'm sure you'll find as did I that all beer tastes better in paradise. I whole heartedly support the opinion of La Haina being a very good time, and if you travel the road to Hana I strongly suggest taking a bus tour.