Task lighting in a kitchen is most often found under the upper cabinets. The type of light used for under cabinet lighting can be fluorescent, halogen, xenon or incandescent. Fluorescent is the most economical, both in initial cost and operating cost. One drawback is they cannot be dimmed. For some people fluorescent just doesn't fit their taste. Both halogen and xenon can come in several types of fixtures. These can be puck or button lights, individual fixtures of various sizes and low voltage linear track.
Puck lights are my least favorite type of under cabinet lighting. In some cases however, where there is a flat bottom type cabinet with a hollow space they are well suited. One problem with these is they tend to create a spotty appearance of light. The bulbs also seem to burn out fairly quickly.
Individual fixtures work well and if they are installed near the back the wiring is hidden. These types of fixtures usually come in both halogen and xenon. The better bulb is xenon, they burn cooler and last longer. They come in different lengths so there is some compromise to make them fit. Fixtures like this come with a switch on each unit and sometimes even a high and low.
Lastly there is low voltage linear track lighting. This is a custom lighting job. It is a bit more expensive than the other methods but in my opinion well worth it. With a linear track the light can cover end to end since it can be cut to fit. It is very low profile and uses xenon bulbs. Because the bulbs are open they disperse light at more than 180 degrees, which gives great coverage. This type of under cabinet lighting is my first choice.
Whichever style of task lighting you choose, consider having a wall switch installed to control them. It is far more convenient than going to each individual unit and turning them on or off. See the links below for more information.