This was Dave's drink of choice at Margie Gras - Labor Day 2008. Cool and crisp, but unlike most drinks of this sort the ginger keeps it from being cloyingly sweet. 

2 oz. white rum
2 slices fresh ginger
3 oz. cranberry juice
3 oz. pineapple juice

Shaker, muddler, ice, highball glass

1. Pound/muddle the ginger and run together in the bottom of a shaker.
2. Add ice and the remaining ingredients.
3. Shake and strain into a highball filled with ice.

You can, of couse, do the muddling at the bottom of the glass, add ice, and pour the rest of the juice in. You'll end up with bits of ginger in the drink, but that's not that bad of a thing.

Source: Ben Reed, Cool Cocktails.