Icloud

iCloud (formerly iTools, .Mac and MobileMe) is a cloud computing service  from Apple Inc. announced on June 6, 2011 at the Apple Worldwide Developers Conference (WWDC). The service allows users to store data such as music files for download to multiple devices such as iPhones, iPods, iPads, and personal computers running Mac OS X or Microsoft Windows on computer servers owned by Apple. It also replaces Apple's MobileMe program, acting as a data syncing center for email, contacts, calendars, bookmark, notes, to-do lists and other data.iCloud is so much more than a hard drive in the sky. It’s the effortless way to access just about everything on all your devices. iCloud stores your content so it’s always accessible from your iPad, iPhone, iPod touch, Mac, or PC.* It gives you instant access to your music, apps, latest photos, and more. And it keeps your email, contacts, and calendars up to date across all your devices. No syncing required. No management required. In fact, no anything required. iCloud does it all for you.
UPTPDATE:
 Apple has reveled the pricing for its upcoming iCloud service.iCloud comes with 5GB of storage as part of the free package. 5GB might not sound like a lot, but remember that this doesn’t include your music or photos in your photo stream (which only stay active for 30 days).
Want more storage? No problem! Here are the US costs for the upgrade.

• 10GB (15GB total) - $20/year
• 20GB (25GB total) - $40/year
• 50GB (55GB total) - $100/year

Here are the UK prices:

• 10GB (15GB total) - £14/year
• 20GB (25GB total) - £28/year
• 50GB (55GB total) - £70/year

And here are the European prices:

• 10GB (15GB total) - 16€/year
• 20GB (25GB total) - 32€/year
• 50GB (55GB total) - 80€/year

                                                                                                                                                      
Features:
The cloud-based system allows users to store music, photos, applications, documents, iBooks and contacts, as well as serving as a platform for Apple's email servers and calendars. According to InfiniteApple, iCloud "simply manages links to uploaded content" hosted in turn by Microsoft's Windows Azure and Amazon Web Services.Each account has 5 GB of free storage. Purchased music, apps and books and the Photo Stream service will not reduce this free space. Any music files purchased via iTunes are automatically downloaded to any registered devices e.g. iPods, iPhones and computers. When a user registers a new device, all iTunes content can be automatically download.