Paul Thurrott got some exclusive information on the new Vista RC1 (Release Candidate 1) release date. It has now been pushed back from August 15 to early September (around September 7). As of right now it looks like the build will be Vista 5520 which has not had any screenshots leaked as of right now.
He also goes on to discuss the release to manufacturing (RTM) build as being from a September escrow of Vista. The final version will then be released on October 25.
Longhorn Server Beta 3 is expected in the first quarter of 2007 and a final release should be seen sometime in the second half of 2007.