The other day Blizzard quickly shut down their beta servers because they accidentally allowed non-beta players access to a "Diablo III" starter edition. (Read more about that here)
Today, Blizzard announced an "open beta weekend" for players!
From Friday, April 20 at 12:01 p.m. PDT (noon), until Monday, April 23 at 10:00 a.m. PDT you can log onto their battle.net account and download the Diablo III client. The only catch is that you can only level your characters to 13. Click the link below to read Blizzard's blog about it:
Blizzard Blog: Diablo III Open Beta Weekend