A german company 'Torqeedo' has recently (Feb 2009) added a kayak motor to it's electric outboard line. Their claim: "The first genuine kayak motor".
Ultralight electric kayak motor for most rigid kayaks; for kayak fishermen, or as a power reserve to cope with currents, winds and to increase range.
An outboard suitable for kayaks needs to meet very special standards: It must be extremely light and also watertight. The motor needs to fit onto almost any kayak. It must be faster than a kayaker can paddle, and provide a worthwhile range.
The result of these challenges is called Ultralight, which meets all these demands. It weighs only 15 lbs including battery.
Safety: The motor shuts off when the magnetic key on the remote throttle control is removed. Therefore, for safety reasons, the magnetic key should be attached to the wrist or the life vest. If the kayak capsizes, the motor shuts off automatically to avoid possible injury. 
Lithium-manganese battery life expectancy: Charge cycles are not the main factor affecting the service life of the lithium-manganese battery. The battery does not have a memory-effect. Generally, a loss of capacity of 4% per year can be assumed. Aging is accelerated if the battery is exposed to high temperatures for long periods and if it is stored fully charged for long periods. Therefore, the battery can be used in very hot conditions, but should be removed from the sun and stored in a cool place when not used. If it is stored for a longer period of time, its charge status should be about 50%. If these instructions are followed, your battery will have a life expectancy of some 6-10 years. 
Mounting ball attaches onto the top of the kayak. Ball-and-socket joint adapts to different kayak shapes. Only the small mounting ball is fixed permanently to the boat, the motor with all the other parts can be easily removed when not needed. - Extremely high-efficient drive train, performance comparable with 1 hp gas outboard (cable from outboard to battery 78.74 inch).
- Auto kick-up feature to protect from grounding.
- Attachement point for a line to manually tilt the motor.
- Attachement point for the "reverse drive" line (only necessary to revers).
- Connection to kayak steering / steering lock mechanism.
- Lithium-manganese high-performance battery with integrated GPS-receiver.
- Remote throttle control with magnetic on/off key and information display (incl. cable 59.06 inch).
It apears this unit would attach to almost any wooden kayak nicely.
Torqeedo: Product description$1,799 at Jamestown Distributors
