I agree with Ubuntu, but also try Mint - it is ubuntu with all codecs and so on already installed!
http://linuxmint.com/
If you do use ubuntu, go to the software centre and install the restricted extras package - that will give you most of the codecs you need.
A good place to look around is
http://distrowatch.com/
The thing I have against Ubuntu is that they are becoming the microsoft of the opensource world. Just keep in mind that the unity interface is not really in line with the general linux experience. Most desktops (like gnome or xfce or cinnamon etc) enhance the overall computing experience, whereas unity is trying to cover many bases such as computing on your TV and smartphone, while using a common interface.
So, if you do not like the interface, try another one! KDE is awesome too...
Almost any Ubuntu or Debian based distro will have awesome software repositories that make it a pleasure to use.