If you've got room on your drive or in your garage for another car there's easy money to be made.
Websites such as ParkatmyHouse.com or YourParkingSpace make it easy to make money out of your spare parking spaces. Simply register and enter the details of the space, including full address, availability and facilities (such as lighting at night) and then set your price. The websites will do the rest.
Obviously it's all about location with spaces near train and tube stations being most desirable. Admittedly these websites do take a % of the money you earn but with ParkatmyHouse claiming that most people letting out their space can expect to earn around £30 a week (some prime spots are earning over £3,000 a year) it is well worth the effort.