Google on Monday launched a holiday site featuring retailers that use its Checkout payment service and unveiled money-back promotions to lure customers.

Similar to eBay's popular PayPal service, Google Checkout, which launched in June, provides a single avenue for making purchases on multiple retail sites, rather than inputting shipping addresses, credit card numbers, and other information on each site. Clicking the Checkout link on the sites of participating merchants accesses the service.

PayPal is the largest online payment service, but Google is looking to add customers through promotions that include $10 off purchases of $30 or more through Dec. 26. For example, if shoppers visited five participating merchants and spent between $30 and $49 on each site, they would get back a total of $50. The credits are automatically applied as purchases are made, but not all merchants offer the discounts.

For shoppers who wish to give to charity during the holiday season, Google will add $10 to every Checkout user's first donation of $30 or more to any one of eight international organizations.

Meanwhile, in a Google-commissioned survey of consumers, Harris Interactive found that 40% of employed U.S. adults plan to do at least some of their online holiday shopping from work this year. Fully one in four of those shoppers are expected buy gifts on Cyber Monday, which refers to the Monday after the Thanksgiving weekend. Cyber Monday, however, is not the busiest online shopping day of the year, which is usually closer to mid-December.