Microsoft has agreed to acquire a Connecticut-based research company called Greenfield Online, which runs both a website called Ciao for European comparison shoppers and an online survey system that helps businesses conduct market research.

The cash tender offer to buy out all of Greenfield’s outstanding shares amounts to roughly $486 million, about $60 million more than investment firm Quadrangle recently offered to pay for Greenfield. Microsoft has already found an unnamed party to buy Greenfield’s surveys division from it, leaving the Redmond, WA-based company with the remaining Ciao subsidiary.

Ciao is a consumer-oriented website for (mainly European) shoppers who want to find reviews, ratings, and price comparisons for goods they can buy elsewhere online. To get an idea of the service, check out this listing for a Canon Powershot camera where you’ll see prices aggregated from several online retailers and reviews posted directly to Ciao itself. According to ComScore, Ciao receives over 26.4 million unique visitors per month from seven countries.

Microsoft’s decision to acquire Ciao is reminiscent of Yahoo’s decision to purchase Paris-based Kelkoo in 2004 for about $670 million – one that Yahoo has since reconsidered.

As with its purchase of discount shopping site Jellyfish last Fall, Microsoft plans to integrate Ciao into its Live Search offering, this time as a means to beef up its offering for European users.

Ciao was founded in Munich in 1999 and purchased by Greenfield Online in 2005.