Express.com edged into the top spot by less than one point with high scores in usability and service in the latest PowerRankings of online movie sellers by Forrester Research, Inc. (Nasdaq: FORR). Forrester PowerRankings combines survey data from online consumers and unbiased shopping tests to provide objective rankings of the leading US eCommerce sites. The companies that rank below Express.com are Amazon.com, 800.COM, buy.com, and CDnow.com.

In a tight two-way race, Express.com snatched the lead from Amazon.com, while the rest of the pack trailed behind. Express.com should thank its customers, as it virtually tied Amazon.com in the Forrester’s shopper battery of in-depth tests. But Express.com’s higher marks from consumers — particularly in service — determined the outcome. In addition, Express.com’s privacy policy is prominently displayed for first-time shoppers, its three-step express checkout is quick and easy to use, and the site has detailed inventory information.

Amazon.com offers the fastest shopping experience for repeat buyers as well as multiple ways to search for the perfect film, but unlike Express.com, the site offers vague inventory information, and its customer support phone number is almost impossible to find.

“This is the second time reigning champion Amazon.com was beaten in an updated category — first in books and now in movies by Express.com,” said Tom Rhinelander, senior analyst at Forrester Research. “In the spring, Express.com was ranked No. 2, but this time around it won by a slim margin. The win demonstrates that Amazon.com’s advantages over its strongest competitors are diminishing.”

800.COM finished third, thanks to inexpensive shipping prices and good customer phone service, but the site lacks express checkout for returning shoppers, and it had numerous problems displaying online order status during testing. Fourth place buy.com is easy to use but still offers fewer features than its rivals do and only offers customer reviews and ratings for some films. While last place CDnow.com’s customer support is incredibly fast to pick up the phone, selling movies appears to remain an afterthought on the music-oriented site.

For the latest PowerRankings, Forrester surveyed 20,000 consumers from the NPD Group’s online panel. These consumers identified the most recent eCommerce sites that they purchased from and rated their experiences. A team of Forrester shoppers then evaluated the shopping experience for sites with a statistically valid number of consumer respondents, performing a series of rigorous tests. The consumer data and Forrester shopper scores were then synthesized and weighted, with consumer views accounting for two-thirds of the overall PowerRanking. A complete set of PowerRankings results — both consumer and Forrester shopper data — is made available to all ranked companies at no charge.

In the coming weeks, Forrester will be announcing results in additional PowerRankings categories. Additional information about each of the categories, including a complete set of rankings and scores, can be found at the PowerRankings Web site — powerrankings.forrester.com.