Many new homes are designed with locations for ceiling fans specifically planned. However in most cases, when a homeowner buys a ceiling fan, it is to replace an existing light fixture, and so the ceiling fan has to double as a light fixture. For this reason, ceiling fans were designed to be able to accept a light attachment.
Most ceiling fans already include light fixtures for this reason. The most common design holds three or four 60 watt bulbs, some have a single globe (usually also 60 watts), some more modern designs include built-in halogen lights. In some cases, if you wish to use the fan without a light fixture, it can be removed and a decorative cap put in it’s place. However in some fans the light is permanently attached and cannot be removed, so this is something to check when buying a fan.
Most fans that are sold without a light fixture can accept an accessory one. This gives you a wide variety of options, light kits come with anywhere from one to siz 60 watt bulbs, in styles from Victorian tulips and crystal to modern spotlights and neon. Fluorescent lights are also available. If a fan includes a light kit, usually that light kit is the only option for that fan and it can not be exchanged for a different one. So if you intend to purchase a separate light, purchase a fan that does not include a light.
Most fan lights, particularly those built into the fan, are also limited by wattage, so make sure the light provided will be bright enough for the room. Most fixtures use the appropriate number of 60 watt bulbs, but some more decorative built in lights (stained glass, uplights, etc.) use lower wattage candelabra bulbs and are more for decoration and ambiance than general purpose lighting. In the case of regular bulbs, you can replace them with compact fluorescence to obtain more light, so long as they are not controlled by a remote or dimmer. See “ceiling fan faq” for more information.