According to Wikipedia, a drink invented in the United States in 1941 to sell vodka. Mules were drinks made with ginger beer. Traditionally served in a copper mug, but this tradition was a marketing gimmick so mine isn't.
Vodka
Rose's Lime Juice (originally lime juice but I always have Rose's around for making my own sweet and sour)
Ginger Beer
Lime garnish
Pour an ounce of vodka over ice, add a couple tablespoons of lime juice, and fill with ginger beer. Garnish with the garnish.
It is really good.
PS When drinking any alcohol, don't buy the cheap crap. Smirnoff's is NOT good vodka. I am not a big fan of Russian Standard as I think it has a chemical aftertaste. I find Stolichnaya to be nice and smooth, Wybrova is incredible but there are only two places in the United States where you can get it.