Here's a list of sites giving away beta keys in some competitions.
First off heres another good thread being kept up to date on diablo.incgamers.com:
From Inc Gamers Forum:
Hunter starcraft 2nd Beta key!
Chrisek has a key to give away if u follow on twitter and retweet... pretty high demands.. kinda annoyed to have to follow people i dont care about but w/e.
tenton hammer contest - See link for details
Diablo Fans Caption Contest See link for details. Take a pic, add captions win beta key. repeat. Note: unlimited submissions?
OMFGCata Youtube - Impersonate Decard Cain lolol should be funny.
Force Stratagy Gaming on You tube -7 keys. Giveaway complete Friday Oct. 7 12:00 PM EST:
Blizz Planet - UPDATED - See link.
If you come across anything please PM me and I'll add to OP