(Listing mode: latest news first)
2010-12-20: X11R7.6 released
2009-10-26: X11R7.5 released
2009-02-01: Results of Google/X.Org Summer of Code 2008
2008-09-23: X11R7.4 released
2008-03-20: X.Org takes part in in Google Summer of Code 2008
2007-09-06: X11R7.3 released
2007-02-15: X11R7.2 released
2006-05-22: X11R7.1 Released
2006-03-20: xorg-server 1.0.2 Released
2006-03-20: X.Org Security Advisory: privilege escalation and DoS in X11R6.9, X11R7.0
2005-12-21: X11R6.9 and X11R7.0 Released
2005-02-11: X11R6.8.2 Released
2004-11-17: X.Org Foundation Security Advisory For The X Window System
2004-09-17: X11R6.8.1 Released
2004-09-09: X11R6.8.0 Released
2004-05-07: XDevConf 2004
2004-04-24: Ongoing development moved to HEAD
2004-04-08: X.Org Foundation releases X11R6.7.0
2004-02-25: Report on platform compatibility
You can find a bit more X11 related news at freedesktop.org's News page.
You can find more detailed info on the releases at XorgReleases.