A few drinks that get mixed often by my cadre of serious drinking friends:
the Atlanta: A manhattan spiked with a squirt of coca cola.
a George Jones: A screwdriver topped off with champagne (or some other bubble substitute)... i.e., a mimosa for people who really want to party. looking back, a pitcher of this drink alone has saved more than a few lame parties I've had to endure.
the LP: Southern Comfort and pineapple juice (same mix as a jack and coke). It gives off a simultaneously sexy and obnoxious "I'm so class I can be trashy" sort of vibe.
Honestly, all these sound absolutely terrible, the last one isn't even a cocktail, and none of them sound like something I'd want to drink in a restaurant.
There's not really a lot of room for experimentation with the classic straight spirit cocktails. Most of the good combinations have already been invented, and even the variations are famous enough in their own right. If your job is actually to invent a new cocktail, and not just rip off an old one, there's a few areas of cocktails that have almost unlimited potential however and while most combinations have been tried, few are famous enough to really worry about ripping off.
1) Fruity cocktails. Grab some white rum, a good dark rum, some vodka, (hell maybe some Gin if you're feeling
sassy) some Cointreau, some Blue Curaco, and some of the other liqueurs with fruit flavours like Grenadine, experiment with these and various combinations of fruit juices. Women love fruity cocktails and you can do cool shit with layering that they go crazy for.
2) Milky cocktails. This one is a lot harder to do and a lot easier to fuck up, but if you have the time, inclination, and resources to experiment, have a crack at it, you can make some really good cocktails with milky ingredients. Baileys, Kahlua, white and dark creme de cacao, maybe some amaretto or Frangelico, milk, cream, strawberries, use your imagination.
Remember that while you typically shake these sorts of cocktails, you can always just build them over ice for a different texture, which also allows you to make extremely pretty, presentable drinks if the ingredients are different enough colours, which a lot of people value almost as highly as the taste in the first place.
Incidentally, while you don't really make shots in a restaurant I am guessing, I just wanted to share a shot my manager makes me sometimes. He is fucking batshit crazy for chartreuse and every-time he makes me a drink he makes me something with it in it. Once he ordered a bunch of us shots of Chartreuse topped with tobasco (which actually helped the taste I'll admit) but the other night he actually made me one that was really good. He called it a Three Wise Men on Acid, and is basically Jack Daniels, Johnny Walker and Jim Beam in a shot, topped with Chartreuse.