Anchor Steam, Summit, Schells, Leinekugel, Boulevard, Big Sky are the breweries that I seem to go back to most often because they are what are available around here (SE South Dakota). I'm surprised I haven't seen anyone mention Fat Tire (though I may have skimmed past it), its a great ale out of Colorado but unfortunately is unavailable where I live, though it is sold in Minnesota, Iowa and Nebraska.
Stouts, Porters, Pale Ale, IPA, Hefeweizen are probably the styles I go with most often, the first two in the winter and the other three in the summer. I'm not above drinking a cheap light American lager, but I only do this when I am trying to get drunk or nothing else is around. You drink them cold so you don't have to taste them and they aren't as filling so you can drink even faster. This is self destructive on many levels so I don't suggest doing it too often.
In general ales should be consumed at cellar temperature 50s to 60s F. Lagers should be served cooler than that (40s F, sorry I don't do metric). Very few beers should be served at room temperature and frosty mugs should never be pared with a good tasting beer.