Centos 6 is probably the best free Linux system available, largely because of it's compatibility to RHEL. The support is there for pretty much everything if you know where to look and in it's minimal incarnation, (I use it with just Fluxbox, Thunar and Rxvt
) it is very fast, much faster than the equivalent Ubuntu, Debian etc. The multimedia support is actually fine with codecs for everything freely available. It is easy to find information on pretty much all aspects because you not only have Centos but also RHEL documentation. The repos work together if you set up yum priorities properly and there is now quite a substantial choice available. Dropping it down to a server is quick and it performs well. Centos 6 has pretty much all you need, not just in Server or Desktop mode but as an all encompassing computing workstation.
You can put it on Netbooks, Laptops et al and get it up and running quickly. The Live version is great for rescues or quick boot ups and detects wireless connections easily.
There are others of course but Centos 6 takes some beating for a free Linux distro.