In a either a lowball or highball glass, add ice, gin, and a dash of lime juice. Stir, garnish with a lime wedge, and top the glass off with tonic water.

Alternatively, go hog-wild:

http://www.washingtonpost.com/wp-dyn/content/article/2011/02/15/...

Or even make them into gelee:
http://kennethalan.blogspot.com/2008/07/gin-tonic-gele-shots.html