CNet reports that the next time you're in the market for a cute, cuddly Shih-tzu, or a 1993 Chevy truck, or a three-bedroom, two-bath house in Maryland, you think Walmart. The big-box retailer is actually testing the waters with a beta of free online classified ads. The site, launched last week and powered by Oodle.com, carries more than 40 million listings because it taps into Oodle.com's already-existing postings. Walmart's free service allows sellers and buyers to post and search for items in seven categories and in major U.S. cities. The effort is a direct challenge to Craigslist, which offers free ads with the exceptions of job postings in some cities and brokered apartment listings in New York City.