For summer cocktails on the tarter side, there's La Paloma - grapefruit soda, tequila and lime juice. I use the San Pellegrino Pompelmo, but use the one you like best.
I'm also a fan of the Badminton Cup. This is something they used to serve at Greyz and I finally figured out how to replicate the drink: 1 ounce lime juice, .75 oz simple syrup, 2 ounces of gin, 4 or 5 slices of cucumber, 7 or 8 mint leaves. Combine everything but gin and muddle cucumbers and mint, add ice and gin. Shake vigorously and serve. You can add a splash of seltzer if you like. The drink has a lot in common with the cucumber collins.
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