Source for the latest release can always be downloaded from http://www.busybox.net/downloads/.
Each 1.x branch has bug fix releases after initial 1.x.0 release. Latest releases for each branch: 1.9.1, 1.8.2, 1.7.4, 1.6.2, 1.5.1, 1.4.1, 1.3.2.
You can also obtain Daily Snapshots of the latest development source tree for those wishing to follow BusyBox development, but cannot or do not wish to use Subversion (svn).