RAR is not UNIX specific anyway, as I have a Windows using friend who uses it all the time. The nice thing about it is that you can split the archives up, so when you have "an extreme case of HUGE file sizeness" you can make say, 25 5 meg files instead of one 125 meg file for easier download.
I don't know if stuffit can do this, but DiskCopy can (make a compressed .dmg or .smi in a few parts).
Stuffit is readily available for Mac OS, Mac OS X, Windows, Linux and Solaris, but only comes pre-installed on Macs.
If you are targetting the mac demographic specifically, also try Disk Copy for a compressed .dmg or .smi file, as they tend to work wuite nicely.
--PB