Wal-Mart has exited the online DVD rental market, partnering with Netflix. Wal-Mart will refer all their DVD rental business to Netflix, and Netflix will refer all DVD sales to Wal-Mart. Wal-Mart's exit leaves only Netflix and Blockbuster as major players in the game. It is rumored that Amazon has a product in the UK and may offer the service in the US later this year.
For a previous review of online DVD rentals, see this link.