The Engineering Windows 7 blog posted a list of changes that are going to be incorporated in the Windows 7 Release Candidate from the feedback received during the beta.

My personal favorite are in Media Player where they are going to improve the Internet Radio Playback, and they have support for .mov files out-of-the-box without having to download QuickTime from Apple and the Apple Software Updater, etc.

Improvements to the headphone experience and increased audio reliability. I had issues audio reliability with audio switching accurately with using a speakerphone, headset and the computer speakers. This should be fixed in the RC.

You can see the complete list of the 36 changes being made here: http://blogs.msdn.com/e7/archive/2009/02/26/some-changes-since-beta.aspx