A Mac comes with a number of ways to compress a file. You can use zip very easily, you can pop open a command line prompt and use tar and bzip2 for very good compression.
I use a third party utility, StuffIt. Mainly because it offers a couple niceties for long term storage of archives. First, is the fact that it can store error correction data with the archive. This means that if something flips a couple bits somewhere in the file, there is an excellent chance of no damage happening to the contents, unless the damage is more than what the error correction can fix. It also has decent encryption.