Wal-Mart's Vudu movie download service has rapidly become the third most popular in its field, putting it ahead of similar services from Amazon and Sony and behind only Apple's iTunes service and Microsoft's Zune Video Marketplace, the Wall Street Journal observed today (Monday). "The business we're in today, offering first-run movies a la carte, is doing very well right now and has tripled so far this year," Vudu General Manager Edward Lichty told the newspaper. Unlike Netflix, which only offers rentals, Wal-Mart's Vudu offers both movies to own and movies to rent. Customers can access the movies via either Wal-Mart's own website or via Vudu.com, which Wal-Mart purchased last year for about $100 million as a way of countering a huge fall-off in DVD sales. (Wal-Mart is the largest retailer of DVDs and Blu-ray Discs.) Wal-Mart has traditionally sold DVDs and cut-rate prices -- sometimes even at a loss -- as a lure to bring customers into its stores. But Dan Cryan, a senior analyst at IHS, cold the Journal that it's not clear yet how Wal-Mart intends to tie online movie sales into its core business.