WinDVD, etc. came with my computer but there is one player I use and have always used to play anything and everything: VLC Player. If you don’t know about it, only go to that link if you’re not really that of a oh-I-want-everything-neat-and-tide-hey-whats-that-thing-there-on-the-scroll-bar-oooh-they-haven’t-done-a-good-job-on-that kind of a guy because its UI isn’t really that great, but considering its free and if you’re a geek only then will you understand that it plays anything and everything, it’s my choice of a player.
Now, moving on from the praise-the-player bit, John Battelle has news that Google launched a web-based video playback feature based on VLC. I can certainly see why they chose VLC, but it’s also great to see them involve in open-source as a whole thing. If you’re interested (I know you are!) here’s the link to get it.