Until Monday, April 23 at 1:00 pm ET, Blizzard offers the Diablo 3 Open Beta for Windows and Mac for free with via the directions below. (You'll need a valid Battle.net account.) That's the first beta offer we've seen for Blizzard Entertainment. The retail game is expected for release on or around May 15. To play the beta:

1. Sign into or create a Battle.net account by clicking here
2. download and install the Diablo III Beta client for Windows or Mac
3. log in to the game using your Battle.net account name and password, and play