Not the best, but possibly the most memorable bar I've ever been in (for the bar itself, not for what went on there) was the bar at the town of Mine #5 in northwestern PA.
Obviously, the place was built around a mine, now long closed and probably doesn't exist. The main building in town was a large (4 story ?) clap board building that held the company store, restaraunt, bar, rooms and I do believe house of ill repute. As near as I could tell at the time, the bar was the only part still being used.
The bar itself was long enough to hold an entire shift of miners and I still haven't seen one to equal it. If it hasn't rotted or burned, it'd be worth a lot of money.
The only way I got in there was a college professor wanted to show it to me. One drink, a look around and we left.