1. Incandescent, as in a typical light bulb. They tend to have warm color, are the cheapest to buy, but are relatively inefficient.
2. Halogen bulbs are a type of incandescent, but they are somewhat more efficient. They are particularly useful for spot or task lighting since they are a very intense and focused light.
3. Florescent tubes have been commonplace in institutional settings for many years. Newer compact florescent tubes have addressed the concerns of size, noise and color and are gaining acceptance in residential applications. There are still issues with installing them outdoors in cold environments, and with using them with dimmers. Florescent lighting is the most efficient residential lighting, but more expensive to buy.

The efficacy of lighting is typically expressed as Lumens per Watt (LPW, or the amount of light given off, for a unit of energy). Incandescent bulbs top out at 22 LPW for halogen type bulbs, whereas florescent can go as high as 80. So if 10% of you energy bill is lighting (a typical number according to the US Department of Energy) and we can reduce that by 60% by changing to compact florescent lights, that could be as much as $60 on a typical $1000/year bill.

But first make sure you have the right amount of light, turn lights off when not using them (florescent lights should be left on if you will be back within 15 minutes), then change to florescent wherever possible. The added benefit is that they last 3-4 times longer than standard conventional.

If you have an application that doesn't suit florescent, halogen last longer, and are more efficient than conventional incandescent.

If you want to get really fancy then consider motion detectors and other home automation products to automatically turn lights on and off.

We didn't talk in this article about LEDs (light emitting diodes). LEDs are small solid bulbs which are extremely efficient, durable and long-lasting. Because they don't have a filament, they are not easily damaged. They can stand up to incredible abuse. They also last 10 times longer than compact fluorescents and well over a hundred times longer than typical incandescent bulbs. At present, their common application seems to be limited to single bulb use in such things as electronics, instrument panels and more recently Christmas tree lights. Many cities are replacing incandescent traffic lights with LED arrays because they can reduce electrical consumption by as much as 80%. At this point they are not commonly used to replace every day lighting. The cost is still prohibitive, but it is just a matter of time.