Sometimes, but NOT always, compression with 7z can make a smaller archive.
It supports several formats but defaults to LZMA.
7z home page: http://www.7-zip.org/7z.html
There are 3 Mac packages with a universal binary for 7z. But one is old, from 2006
For the other two:
You can get the binary from here: http://homepage.mac.com/krmathis/applications/p7zip%204.47.dmg
Or, download the following package and go to the internal Resources folder to get the binary:
http://savefile.com/files/17121
Both are the same and compiled June 10, 2007