USATODAY.com - Ebay makes a business of its online auction data:

"SAN FRANCISCO (Reuters) � Ebay has begun selling the price data generated by its popular Internet auction site in the hope that such information will set a benchmark for the value of a wide range of goods, a company executive said Monday.
The Silicon Valley company, which has been the trading venue for everything from a California town to used office supplies and cars, tracks sales in the more than 27,000 auction categories on its online marketplace.
This year it quietly began licensing that information to about 20 customers, who each pay $10,000 a year and up for access, said Randy Ching, vice president of platform solutions at eBay."