I normally just drink rum on it's own if it's a brand I like... You could always mix it with cola and a slice of lemon/lime for a Cuba Libre. You can also drop a shot glass with rum into a pint of beer and down it like a submarine...
Try this if you've got a bit more cash: 1 shot dark rum, 2 shots malibu (coconut rum), pineapple juice, crushed green apple, simple syrup (sugar and water boiled down).
method: Muddle (crush) a slice of green apple into the shaker, add a little ice, alcohol, syrup, and top with juice. Shake for 3 secs. Serve in a Tom Collins glass with a red apple peel spiral haning off the edge of the glass, bendy straw, and pineapple slice.
I really shouldn't be giving away recipes :/