A Sidecar is another classic that any bar should have the ingredients to make, even if the bartender doesn't know what it is off the top of his head. It's simply,
2 parts brandy 1 part Cointreau (or triple sec) 1 part lemon juice
Shaken and served straight up with either a twist of lemon or a lemon wheel.
That does sound like it could be a real winner. I'd like it more if it had more alcohol, though. I might experiment with tossing some brandy in there as well to make it a slightly more exotic Brandy Alexander (0.75 oz brandy, 0.75 oz cream, 0.5 oz creme de cacao)