Skuuudle - Discover, match and monitor your eCommerce competitors.
SimilarWeb - SimilarWeb.com is a website analysis tool that gives you analytics information for any website.
Price2Spy - Price2Spy is a price monitoring, pricing analytics, and repricing tool, meant to help eCommerce professionals keep an eye on their competitors or retailers.
Website Informer - Website.informer: complete data lookup & free aggregated report on any domain including whois, visitors, IP & DNS details, competitors, owners, etc
Prisync - Prisync is a competitor price tracking and monitoring software for all sizes of e-commerce companies worldwide.
Site Rank Data - View historical rank information of websites via time series charts.