The creative use of lighting can greatly enhance the feel and appearance of a kitchen and should be practical as well as decorative.

Certain work areas, such as hobs, sink and food preparation, require good efficient lighting. However these can be independently controlled and adjusted so as not to intrude in the overall effect of the kitchen.

Other areas can have low-level lighting; possibly hidden strip lights under wall cabinets, and again can be independently controlled.

Interior cabinet display lights, popular on glass-fronted units add a nice touch.
If you do fit these don't forget to fit the unit with glass shelves otherwise the light will only illuminate the cabinet as far as the top shelf, the result being the top half of the cabinet will be lit & the bottom half unlit.

If you intend to use the kitchen for eating, think about a light over the table, which can be adjustable for both height and intensity.

Halogen lights are popular at the moment; these can either be powered straight from the mains or low voltage with a transformer (when positioning the transformer it is unwise to place it where it will be difficult to access in the future for maintenance).
As with all lights ensure that the lights are powerful enough to provide adequate lighting for the area Low voltage 20-watt lights are suitable for secondary lighting but will not be powerful enough to light the room.

When fitting lights above wall units or windows to create a lighting canopy system remember to infill the space between the lighting canopy board and the ceiling. Otherwise an up lighting effect will cast shadows & colours across the ceiling of the room. On the other hand some people find the mixture of shadows & colours crated by the lights an attractive, if so leave the infill panel out.

Lighting is a specialist area, take specialist advice and you shall reap the benefits.