There is also DivX which includes a player and a bunch of codecs.
Their are 4 versions of it available but luckily there is a free version, of course your limited with what yoiu can do with it comapred to the other 3. But the codecs are useful....
http://www.divx.com/divx/
click "Download the free DivX Codec/DivX Player bundle" just below the table.
There is also another free version that allows you access to other features but it is Adware support by GAIN. A known spyware so its up to which one you use.