My pretty successful attempt to duplicate a cocktail I had in Paris.

THE EIFFEL SOUR
1.5 oz gin
.75 oz elderflower liquor
.75 oz lime
.5 oz simple syrup
4 slices English cucumber

Muddle cucumber in the bottom of your shaker. Add remaining ingredients and ice and shake until chilled. Double strain into your glass of choice (straight up in Paris, on a nice block of ice in a tumbler at home). You could probably garnish with a slice of cuke if you were feeling fancy.