I lived right down the road from the New Belgium brewery, so I have a soft spot for all of their beers. Fat Tire is the most well known NB beer and is also the most widely available, tap or bottle, but all of their beers are pretty high quality. So, for a fairly widespread domestic, Fat Tire would probably be my choice. It's something that I know I can get in most places when I'm traveling.
As a cold cheep beer, really I'm ok with any of the domestic lights, PBR or a cheap Mexican beer like Corona. I know that they hardly qualify as real beer, but they're perfect if you're doing something fairly active and don't want to be weighed down.
So, widespread domestic: Fat Tire
Cold cheapy: Miller Lite