Dirt and grease coat cabinets over time, so a good cleaning may be all your woodwork needs to make it bright again. Use a commercial cleaner meant for wood, available at a hardware store or home center. Or, mix a solution of 3 tablespoons turpentine, 3 tablespoons linseed oil, and 1 quart boiling water. Wear rubber gloves when mixing and applying the warm solution, and make new batches whenever it starts to cool. Rinse the wood with clean water. Use newspaper or plastic to shield the floor and countertops from spills. If cleaning isn't enough, prepare the wood for paint or varnish by sanding, vacuuming, and wiping with a soft rag soaked in mineral spirits.
If you just want to make your stained wood lighter, bleaching works best. You can use a commercial wood bleach available at hardware stores and home centers. Or, make a solution with 1 part laundry bleach or oxalic acid to 10 parts water. Apply the mixture on a warm day and let it stand for a few minutes (more or less time depending on the amount of bleaching you want). Then wash the wood surface with plenty of water; just take care to keep the water from pooling. While you're working, wear rubber gloves and make sure there's plenty of ventilation. Also spread out plenty of newspaper to protect the floor and countertops from any of the solution that may spill.
If you like the tone and grain of the wood, refinish it with stain and coat it with polyurethane.
Pickling gives you an opaque finish that brings out wood's natural grain, but lets you embellish it with color. Brush on a light coat of flat, oil-base paint. Before it sets, wipe much of it off with a clean burlap rag; the more paint you remove, the more grain you will see. If the paint begins to harden and is difficult to wipe off, remove it with a rag dipped in mineral spirits. To be on the safe side, wipe off more paint than you may think necessary -- you can easily go back and make the pickled surface darker by adding another coat.
Techniques such as color washing, rag rolling, sponging, and stippling will give depth to your painted cabinet finishes. Follow step-by-step instructions to ensure you get a smooth, easy-to-clean surface. More complicated techniques may require help from a professional decorative painter. For a simple way to add more than one color, paint trim or door panels a contrasting hue. (For any painted finish, you must first coat the cabinets' surface with a high-quality primer.)
Consider covering your cabinets with another material, such as urethane, cork, or even wallpaper.