Most distributions ship with Xfce in their own packaging format, but if you want a newer version or you want to build Xfce from scratch, you can find the packages below. Instructions how to compile Xfce can be found here. You can also take a look at the list of Xfce-oriented distributions.
Xfce 4.8 is the most recent version of the Xfce desktop environment. You can find the changes in this release here.
Each package in Xfce can make individual stable or development releases, including the core packages (as described in the release model). You can follow the announcements of the releases on the Xfce users mailing list, watch the release feeds or follow the Xfce identi.ca channel.