7-Zip is extremely useful for automated backups as it has a completely featured command line interface. It integrates into the shell for right-click compression and expansion actions. I've converted a few people at work from WinZip to using this because of it's simplicity and expanded functionality without pay or fuss.
I use 7zip all the time. It's now part of my 'bare necessities' CD for when I do clean installs of Windows. It has a ton of things it -can- do, but it's very easy to install and forget you even have it even though you always use it because of the simple integration into the menu you get when you right-click files.
IZArc can compress and decompress a lot of formats and integrates very well into Windows. It supports various languages and is easy to handle. http://www.izsoft.dir.bg/izarc.htm
Now it even supports archive spanning into files of given size (for floppies, CDs and so on). A must-have for me. I converted to 7-zip from RAR and can admin RAR have some extras, but there is a fee...
7-zip is great in terms of how small it can compress files but the application interface is very awkward. Using the Windows Explorer context menu works well if you don't need to put an archive together from multiple folders.
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