In conjunction with the launch of Windows Phone 7.5 Microsoft has updated windowsphone.com. The new site includes a web-based Marketplace for Windows Phone. The new Marketplace allows you to browse and purchase apps from any PC without the need for software. As an additional benefit, the Marketplace provides a history of your app purchases, giving you an easy way to find apps that you've used in the past.
More than just another app store, the new windowsphone.com also acts as a central point for many of the services that integrate into the phone. Images and documents synched to SkyDrive, as well as your XBox Live avatar and gamer score are prominently displayed in the 'My Phone' area of the site. Microsoft even provides the ability to track your phone's location and gives you the option to ring, lock, or erase your phone in the unfortunate case that your device is lost or stolen.
The new features on windowsphone.com are freely available for all Windows Phone devices, not just those which have received the 7.5 update.