SC2 beta invites are going out. If you opted in before you can check your battle.net account and it might have put you in beta before email informed you. If you haven't opted you can always make a new account at
https://us.battle.net/ and fill out beta preferences (note this is where you also opt in for diablo 3 and everything all at the same time).
Blizzard also said in the beta forums they have lifted any NDA, so everyone is free to share videos, pictures, comments. So if you got any friends in please share links in this thread.