In last week's Fine Cooking post, I listed a simple and easy recipe for a watermelon drink from H. Joseph Ehrmann of Elixir.
The recipe is just cucumber vodka, St. Germain, watermelon, mint, lime, and agave nectar. It's pretty easy for you to make, and even easier for me to make. I can just walk 400 feet or so from my front door and have a bartender at Elixir make one for me.
Also easy are the ways to adapt it. The post contains a non-alcoholic version and lists several spirit substitutions. Please go read it.