I looked into renting my unused points today. David's site mentioned above will pay you $10 a point for any that they are able to find a renter for (they charge $13 to the renter). If the points are within 5 months of expiring, they suggest you offer them at a discounted price, and you would get anywhere from $3-6 for each point that actually finds a renter.
Obviously if you can do it yourself without going through a broker, you could potentially get more.