Google Checkout’s most obvious competitor is eBay’s PayPal service, although the services aren’t identical.

The promotion applies to purchases of $60 or more from participating retailers. That includes better-known outfits such as Buy.com and TigerDirect.com as well as niche sites such as YoYoCrazy.com, Beefjerky.com, PondDeals, and MyHipHopBling.com.

Google mentioned the promotion on its Google Checkout blog on Wednesday.

Google won’t say who’s behind it (um, Google, maybe?), but more than 50 merchants using the Google Checkout service for online payments are offering $10 discounts this summer.