It can be a bit of a pain to search out the good ones. I happen to live in Michigan were we have more micro breweries than we know what to do with, and love bringing stuff from out of state in. There are a lot of "Craft Ale" (Craft Ale is the term we made up when Micro-breweries get to big so Micro sounds silly) breweries that should probably distributed to your local liquor store. I just thought of another fun dark beer, Breckenridge's Vanilla Java Porter. It taste like you would figure from the name.
My advice would be head to your liquor store, and avoid anything that is sold in packs of 12 or greater. If you see a bottle that looks interesting but aren't sure if its worth the cash, check on Beer Advocate (although they are kind of snobs there). That being said an economical choice of decent American Beer is the Sam Adams Variety packs, they make decent beer and with the variety you can really taste around and find what you like. However, I don't think they do dark beer that well.
Yeah, it really bothers me how the popularity of Bud, Miller, Coors, and similar beers gives American Beer culture a bad name. We actually have some fantastic beers! And just to brag about Michigan Beer a bit more, I'm currently in China. Beijing actually and hands down the best beer in town is at a tiny brewery called Great Leap Brewery, run by a couple of guys from Grand Rapids, Michigan.