Personally I'm using the openSUSE distribution, which originally started as German based open-source system SuSE 'System- und Software Entwicklung'. openSUSE is today own by Novell, but is still run as a free opensource free environment.
openSUSE is a great distribution which comes with the choice of several desktop environments and all the software a regular end-user needs. In addition to the standard software packages installed it is easy to install further software in openSUSE if needed.
At this website you will find an excelent online guide with a lot of information about openSUSE and excellent support for the a new (or potential) openSUSE user: www.opensuse-guide.org