Tim Sneath in the team put together a really detailed list of nice features which you get with Windows 7.
He call it his “bumper list of Windows 7 secrets” and is well worth a look. Check at the details here ( http://blogs.msdn.com/tims/archive/2009/01/12/the-bumper-list-of-windows-7-secrets.aspx )
My top one is the new Windows management shortcuts, but there is a whole lot more.