Online auctioneer eBay Inc. (EBAY) on Friday unveiled a new service that not only lists the top-selling consumer products, but also helps shoppers determine their going prices.

The company, working with data analysis start-up Mpire Inc., said it had created eBay Pop, a shopping index service that helps consumers sniff out the collective purchasing trends of U.S. online buyers.

EBay Pop displays sales trends on top items sold on eBay, ranging from music players, video game consoles and hot toys like TMX Tickle Me Elmo to less-obvious products like election memorabilia or the Fisher Price Kid Tough Digital Camera for preschool kids.

"Think of it as a mini-consumer price index for consumer shopping," said Mpire Chief Executive Matt Hulett.

EBay Pop identifies what it calls "movers" — items that have seen a recent price increase or decrease — and "shakers" — those whose sales volume has risen or fallen significantly.

By tracking the two charts in tandem, consumers can watch popular consumer items that are suddenly falling in price.

"It's like a stock market for product prices," said Gartner Inc. analyst Allen Weiner.

Index categories on the site include fashion, tech gadgets, sports, media, toys and "vintage cool" collectibles.

The service has become possible only as major Internet sites like eBay have begun in recent years to allow other companies to create additional services that run on top of their core market functions.

Founded less than two years ago, Seattle-based Mpire runs a shopping search engine on top of data supplied by major e-commerce sites. It has received financial backing from venture capital firm Ignition Partners and former eBay executive Richard Rock.

Like other shopping sites, Mpire makes money when consumers locate an item they want via its service and click to buy it.

EBay became famous nearly a decade ago as the place for holiday-season shoppers to find popular Beanie Baby stuffed animals, but it can no longer count on being the sole destination for shoppers to locate hard-to-find gifts.

It has been slower than other big Internet players like Google, Yahoo and Amazon at adopting the latest generation of "Web 2.0" interactive customer features that encourage audience participation, Weiner said.

EBay is the first company to introduce the Mpire service. Early next year, Mpire will introduce a broader version that works across major shopping sites, including Amazon.com, Yahoo Shopping, Craigslist and more than 2,000 large merchants.