I think one of the most refreshing summer martinis has to be the apple-tini.
I love the bright green color and the way it tastes tart and west like Jolly Rancher candy!
I make mine like this:
Add 2 oz. of DeKuyper's Apple Pucker
2 oz. vodka
and 1/2 oz. of sour mix
to a shaker with LOTS of ice.
Shake till the shaker is too cold to hold anymore.
Strain into frozen martini glass.