Apple will be rolling out iCloud over the next couple of days. Apple has released iTunes 10.5 as a first step today. 

What's new in iTunes 10.5 (From Software Update.)

• iTunes in the Cloud. iTunes now stores your music and TV purchases in iCloud and makes them available on your devices anywhere, any time, at no additional cost.

  • Automatic Downloads. Purchase music from any device or computer and automatically download a copy to your Mac and iOS devices.
  • Download Previous Purchases. Download your past music, TV, app, and book purchases again, at no additional cost. Previous purchases may be unavailable if they are no longer on the iTunes Store.
  • Sync with your iPhone, iPad, or iPod touch with iOS 5.
  • Wi-Fi Syncing. Automatically sync your iPhone, iPad, or iPod touch with iTunes any time they're both on the same Wi-Fi network.