Apple quietly added (updated?) a QuickTime Componenets page last week with plugins to support DivX and Xvid. Xvid is free, but DivX will run you $20. As a relatively new full-time Mac user, the free Flip4Mac WMV plugin was one of my first installs.
(via eHomeUpgrade)
No, the DivX PLAYER is free, just as it is on Windows. It’s the “pro codec” that costs $20, which is only if you want to encode.