You can't go wrong with a gin and tonic but I'm all about Dark N Stormys when I can find the ingredients: Add one part Gosling's Black Seal rum to three parts Gosling's ginger beer. Garnish with a slice of lime. You can substitute the rum or ginger beer if Gosling's isn't available but you'll be missing out.
I'm all about gimlets. 1 part lime juice, 1.5 parts gin, 1 tsp powdered sugar. Really easy to make, and quite good. You can also use vodka. I think both are great. I may be a bit biased since I have a lime tree though.
Gin gimlets are indeed the best, although my personal recipe is for a lot more gin and a lot less lime juice. Usually a rocks glass about three-quarters full of gin (accounting for the volume of a big-ass piece of ice) with a quarter of a lime squeezed in. Haven't tried powdered sugar yet, but I should probably just make up a batch of simple syrup to add here, as it really does add a lot of taste. Can add a bit of fizzy water if you like carbonation, too.
If you use Rose's Sweetened Lime Juice you can safely skip the sugar. Try with Hendrick's Gin for a real trip for your tastebuds.