Individual releases of Xorg modules are here.
6.8.0 post-partum: lessons learned.
For module maintainers: HOWTO Make a release.
X11R7.6 (Released: 2010-12-20) Release Notes. Of note, this release added xorg.conf.d directories, InputClass configuration sections, udev support on Linux, improved documentation, and integrated xcb.
X11R7.2 (Released: 2007-02-15) Of note, this release added autoconfiguration support, and enhanced support for GL-based compositing managers, such as Compiz and Beryl.
X11R7.0 (Released: 2005-12-21)
For more complete information, including a release history, please see the historical releases page.