Google Ad Manager is opening to ALL. Yes, I said all. No more invitations needed for the beta testing.
It is open to everyone having a Google Adsense account.

Here are some of the exciting things Google Ad Manager will bring about:

From Adsense Blog,

"Ad Manager can help you sell, schedule, deliver, and measure both directly-sold and network-based inventory. It offers an intuitive and simple user interface, Google serving speed and reliability, and significant cost savings. Best of all, Ad Manager can be optionally integrated with Google AdSense to offer you an automated way to maximize the revenue of your unsold and network-managed inventory."

Google Ad Manager looks pretty awesome, so what are u waiting for.