Princess sells "Buckets of Beer" where you get 5 bottles for the price of 4 (Bud/Bud Light Aluminum bottles). If you pre-order beer before the cruise, you get 6 bottles for the price of 5 (Becks, Coors Light, MGD, Miller light and Dos Equis).
I think you can get the buckets of MGD, Coors etc... at the bars as well.
I wish they would have a better beer selection but I'm sure its hard appealing to everyone and easier to go with the mass market brands.
I certainly wouldn't mind if they had their own Ale. That would be nice, especially if it was on tap.