The latest stable release is 2013.02, which can be downloaded here:
buildroot-2013.02.tar.gz or buildroot-2013.02.tar.bz2.
The latest release candidate is 2013.05-rc2, which can be downloaded here:
buildroot-2013.05-rc2.tar.gz or buildroot-2013.05-rc2.tar.bz2.
This and earlier releases can always be downloaded from http://buildroot.net/downloads/.
You can also obtain Daily Snapshots of the latest Buildroot source tree if you want to to follow development, but cannot or do not wish to use Git.