Pretty much any American macro lager, including Busch, Bud, Miller, Natural, etc. Unfortunately this stuff dominates the American beer market, giving the many finer brews also called 'beer' a bad name.
Pabst Blue Ribbon, Rolling Rock, and Coors are two generally recognized exceptions, each having a devoted following of discerning tasters despite their budget pricing. Keystone Light also has a devoted fanbase.
One easy way to judge whether a beer is bad or not is by the color of its can. the so called "silver and blues" are generally the bad beers. ie beast, natty, busch etc...
Don't be fooled into believing a beer is necessarily good if it is imported. Some of the overpriced, well-marketed "Euro" beers (e.g. Heinekin) are much better than the American macros listed above.
Sierra Nevada is
terrible excellent though overrated. Try the "Pale Ale", you won't regret it.