Diablo 3's beta will end on May 1, 2012, announced by Blizzard. The developer just added about 275,000 testers into the game last week and there aren't too much time left if you are still waiting for an invitation.
The closed beta allows players to get their hands on part of the content of the first Act. Five characters are available to choose, but the adventure for testers ends after the fight against the Skeleton King.
Each week until the final release, Blizzard will release a new class journeys for each character, and this week you have the Monk.
Diablo 3 will be released on May 15, with the PvP arena feature adding in the future patch.