Good cocktails, should all be easy to look up recipes for:
White Russian - sweet, drinkable and easy.
Manhattan - a real pain to get right, but worth it. Use a decent bourbon.
Martini - my preference is very dry, using Plymouth Gin. If someone says "Shaken, not stirred", punch them.
Margarita - try Cointreau/Grand Marnier rather than triple sec. Always use fresh lime juice, and stay the hell away from Jose Cuervo tequila.
Gin and Tonic - my favourite is using Tanqueray 10 Gin and a wedge of grapefruit.