In an attempt to tighten their stranglehold on American consumers, Wal-Mart has quietly launched a free Internet classified ad service, directly challenging Craigslist, the reigning Internet ad champion. The Wall Street Journal says, “The service, which the retailer described as a pilot test, carries 30 million items, including foreclosed homes, basset hounds, Madonna concert tickets and a 1981 Ford Firebird, as Wal-Mart tapped into Oodle Inc.’s menagerie of listings.” More, inside…