I've noticed a bit of complaining with regards to codecs for some movies (including the latest Sonic 3 video). I'd like to point out a slightly geeky but still easy way to solve this.
GeeXboX is a Linux live CD that essentially turns your computer into a multimedia system.
Do note: Live CD. Nothing is installed on your system, so Windows users needn't worry.
I don't mean to advertise, and I have nothing to do with the project other than as a user. I simply point it out. You boot from the Geexbox CD (really fast booting) and instantly your computer can play virtually any video file. The default disc image doesn't include support for WMP9 or Real Player, though you can add those to your own disc with a bit of geeky workage. Or I could even supply the ISO of my own copy to save people the trouble.
It also plays audio files (probably any kind, but I've only tried with MP3s), audio CDs, video CDs, DVDs, or from a TV tuner card if you have one. It reads from any drive in your system or can even access open network shares. Really handy. And as I said, I have yet to try a video file that doesn't work.
'Course if you like to do other things while watching the videos then this is useless to you.