Margaritas
I made a big pitcher of Watermelon Ginger Margaritas for a 4th of July picnic today. They were a huge hit... if you even remotely care for margaritas, you should give it a try. The ginger gave it a little bit of zing, while the pulpy watermelon cooled off the bite of the tequila a bit.
If you're interested, I've been bookmarking cocktail recipes that I've tried or want to try at http://del.icio.us/kimmie/liquor