Get this player: VLC - (click on link) _ (choose nearest mirror site). Alternate player is MPlayer; MPlayerOSX / MPlayer - The Movie Player

To make it the default of playing video formats, see How to change default program in OSX

There are other options. Such as getting 3rd party plug-ins for quicktime player such as DivX, XviD, 3ivx, etc. And for WMV, Flip4Mac.