If your kitchen is designed using natural materials it should be easy to find a wall clock made in the same or complimentary materials. Stone clocks come in a wide variety of colors and can be made from almost any kind of stone, including ceramics. Steal and metal colored clocks are also widely available, and can range from simple round to artistically soldered works.
Wooden clocks can match cabinets, tables, and chairs, but you have to be careful with the kind of wood used. Certain woods will warp under extreme heat such as can be created in the kitchen. Wood is also an easy material to stain, and a pop of pasta sauce flying out of the [pot in the wrong way can destroy an otherwise elegant dcor item. For this reason getting a faux wood or plastic wall clock may be a better decision to make.
If you can manage to balance creativity with utilitarian design, you can make a truly unique statement in your kitchen using something as simple as a wall clock. Your local yellow pages should be able to direct you to some good resources if you want to go to an actual clock store, and online there are hundreds of sites with a wide variety of clocks available.