The glasses you have available in your bar are completely up to you. If you want a minimal service, at least get some of the glasses in basic section. For a little more style, consider expanding into the optional section. If you can afford it, try to buy quality glassware that makes a nice "ping" when you tap it.

Basic Glassware

Highball Glass Highball Glass: You can use this for mixing almost any drink. A good stand-in for similar looking glasses.
Old Fashioned Glass Old Fashioned Glass / aka. Lowball or Rocks: For shots of alcohol over ice primarily, also for smaller drinks.
Red Wine Glass Red Wine Glass: Use for red or white wine (if you don't have a white wine glass), or water.
Shot Glass Shot Glass: Guess we don't really have to explain this one. Might buy a few extra of these, people tend to get a bit rowdy after continual use...

Optional Glassware

Beer Mug Beer Mug: For beer or beer-shot combinations.
Beer Pilsner Beer Pilsner: This is traditionally for beer, but works well for serving large margaritas and the like.
Brandy Snifter Brandy Snifter: What can we say?
Champagne Flute Champagne Flute: The best way to serve champagne. The bowls allow the fizziness to escape too quickly. Nothing worse than flat champagne...
Cocktail Glass Cocktail Glass: You can use this for serving many different cocktails. In a pinch, you can also use it for serving martinis, but you should really get true martini glasses (no picture available).
Collins Glass Collins Glass: For drinks that require something a bit larger than an old fashioned glass. These look good when frosted before serving.
Cordial Glass Cordial Glass: Generally for concentrated liqueurs...
Irish Coffee Glass Irish Coffee Glass: This makes almost any coffee or other hot drink look good. Generally garnish with whipped cream and chocolate shavings or cinnamon.
Parfait Glass Parfait Glass: Similar to the irish coffee glass, is generally used for drinks with ice cream or fruit in them.
Pousse Cafe Glass Pousse Cafe Glass: Usually used for layered drinks.
Sherry Glass Sherry Glass: Again, what can we say...
Sour Glass Sour Glass: use for sours (see the recipe index).
White Wine Glass White Wine Glass: A bit smaller than red wine glasses with a slightly different shape to the bowl.