If you ever wanted to have a free software that would be able to handle all the different zip formats then you might want to take a look at the open source program called Universal Extractor. Universal Extractor can only be used to extract archives handling this task excellently. It supports a multitude of zip formats including the following popular ones: 7-zip archive, ace archive, arj, gzip, rar, tar and zip archives.
Next to that it can also unpack files from installation packages, it would be no problem for instance to unpack Windows Installer Package files (msi) or unpack the latest Firefox release with the Universal Extractor. It does not make that much sense to use a program like Winrar if you never pack files yourself, a tool that would extract all the archives would be more than enough.
Universal Extractor adds menu entries to the right-click men. You can choose to extract files, extract the archive in the same directory and extract the archive into a sub-directory.
I used to use this one, but I dont like the interface. I got another via http://www.topshop.sk and its fine, I am satisified with this one.