Just d/l it from http://rsync.samba.org/ and compile as follows:
Download and unarchive rsync and its patches
Move patches directory to rsync-3.0.9
Apply patches relevant to preserving Mac OS X metadata
patch -p1 <patches/fileflags.diff
patch -p1 <patches/crtimes.diff
Apply patch relevant to preserving Mac OS X hfs+compression
patch -p1 <patches/hfs-compression.diff
Configure, make, install
sudo make install
Verify your installation
By default, rsync will be installed in /usr/local/bin. If that isn't
in your path, you will need to call your new version of rsync by its
absolute path (/usr/local/bin/rsync).
You can also use a tool like fink or macports to install and manage rsync versions, though the most recent version that fink has is 3.0.8. While rsync is part of the Samba project, which has been replaced with an in-house SMB service, it can be distributed as a separate package.
The GNU licensing was changed to prevent system services from relying on modified versions of the software, which conflicted with Apple's SMB implementation. Apple can still include the software with its OS, which is why it can still keep rsync as a command-line tool that you can use; however, it cannot implement it in ways that if the software is updated or modified by the user then it will break the OS services that depend on it or make it very hard to get them running again. This conflicted with Apple's ability to maintain a quality product, so it changed.
It is entirely possible that Apple can include an updated version of rsync in the future, but my guess is that Apple has its set of BSD tools that works and is not concentrating efforts on updating them for the relatively small crowd that would use them. If it were necessary then Apple would do this, but right now the company is all about iOS and iCloud implementation, and open-source projects are on the back burner.
Pretty much anything under the GNU Public License, including for example the bash shell
To clarify. Anything with a GNU version 3 license. Versions 1 and 2 GNU licensed software versions will most likely continue to ship on Mac OS X.
The GNU version 3 license is very aggressive in how it affect proprietary code forcing the sources to be released. Apple is not interested in making all of Mac OS X open source, so they have been avoiding anything with a GNU version 3 license.
However, you are free to install this code yourself, and as has been mentioned you can download and compile it yourself, or use a package manager such as MacPorts.org or Fink.sf.net
Versions 1 and 2 GNU licensed software versions will most likely continue to ship on Mac OS X.
They may continue to ship, but they won't be updated. All current versions of code distributed by the GNU project are now under GPL v3, and will never be shipped by Apple. The same goes for rsync and Samba (which was dropped from Lion.)