Blizzard surprised us all by launching an open beta of Diablo III to everyone this weekend, April 20 - April 22, for a final stress test on the servers before the game's launch on May 15th.
From Friday, April 20 at 12:01 p.m. PDT (noon), until Monday, April 23 at 10:00 a.m. PDT you'll be able to log in, team up with friends, and play each of the five heroic classes to level 13 as you fight to save the world from the impending demonic invasion.
Download Diablo III Beta
Signup on Battle.net (it's free)
Open Beta FAQ