Shopping comparison sites and services let online shoppers compare products' attributes and prices in a relatively neutral environment. These services also give merchants a channel to market to some of the web’s savviest consumers.

Several companies track and analyze shopping comparison sites including CPC Strategy, Channel Advisor, comScore, and Compete.com. Based on reported revenue generation, traffic, and even ease of use as reported by these various companies, what follows is a list of the ten best comparison shopping tools in 2012.

Google Shopping

Google Shopping is the merger, if you will, of two earlier Google products: Google Product Search and Google Product Listing Ads. Google Product Search — which has been recently closed — was a free service that applied Google’s search algorithms to merchant supplied product data. The service had the best revenue-generating shopping comparison service according to data from CPC Strategy. Google Shopping is part of the AdWords service and provides a pay-per-click channel for product data, including product photography.

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Amazon Product Ads

Amazon Product Ads let merchants place product-specific ads on Amazon category and product detail pages, effectively letting Amazon shoppers compare products. The service works on a pay-per-click model and can be a huge traffic driver. As with other services, Merchants upload product data, set a budget, and receive direct-to-site traffic. It is important to note that this is not part of the Amazon Marketplace. With Amazon Product Ads customers go directly to the merchant’s site and make purchases directly from the merchant, not Amazon.

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Nextag

Nextag might be described as a shopping comparison or price comparison site. Users go to Nextag, search for a product and see results from several participating merchants. This site claims to generate more traffic, more revenue, and more gross merchandise sold than its competition, based on three separate 2010 studies from Compete.com, CPC Strategy, and Channel Advisor.

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Pronto

The Pronto Network offers a number vertical price and product comparison sites, include Proto Style, Proto Home, Proto Tech, Proto Kids, and — believe it or not — Baby Pronto. All told, Pronto lists more than 70,000 million products from some 25,000 merchants, according to the company’s website.

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PriceGrabber

PriceGrabber lets shoppers “find and compare” products from participating merchants across 25 channels, which are essentially product categories. According to CPC Strategy, the typical cost per click on PriceGrabber is just 26 cents, which makes it a relatively good value. PriceGrabber was also on comScore’s list of the top ten fastest gaining web properties in the U.S. for July 2012. The site saw total unique visitors grow 25 percent month over month to a total of nearly 8 million.