You can read the full list here. I've included the new (RTM) items below as well just to show what's coming.
- Enable support for Reporting Services on any server and any port
- Support for SQL 2008 (aka Katmai)
- TFSDeleteProject now permanently deletes (destroys) version control content
- New role for many operations activities - You don't have to be server administrator to run many of the admin utilities any longer
- Enhancements to tfsadminutil - New capability to configure accounts, connections, etc on both TFS and the TFS proxy