Microsoft has published a list on the Engineering Windows 7 blog that details 36 new features and changes that will be present in the first release candidate of Windows 7. You can check it out over here.
For instance, Windows Media Player will now get support for Apple's .MOV video format:
Customers loved the increased range of formats natively supported by the Windows 7 Beta, but noticed areas where they wanted broader support. For example, one was unable to seek to a specific spot in the video in Windows Media Player or Windows Media Center for AVCHD content that was imported from a digital camcorder. We’ve addressed this. Also, while the support for video from some digital cameras worked great, we also got feedback about supporting a broader set of devices out of the box. We’ve since added support for Windows Media Player to natively support the .MOV files used to capture video for many common digital cameras.