A favorite warm weather drink is a Pimm's Cup. Simple, refreshing, dead easy to make. And not so strong as to make you fall asleep directly afterwards (unlike a vesper martini!).
In a glass, I muddled a wedge of lemon and 3 slices of cucumber. The I poured in the Pimms - a couple of ounces or so.....then I added ice (I prefer mine crushed).
Top off with San Pellegrino Limonata and garnish with a slice of cucumber and lemon wedge. Enjoy!