VLC since it seems to play about everything one throws at it. Irfanview for me also picks up what VLC won't play. (WMV I believe)
Looks like VLC is a clear winner with 32%. This program has been around for ages now. Im glad it remained bloat free unlike iTunes and others.
I'm glad that I don't own an iPhone, iPad or iPod so don't have to have that garbage installed on any of my computers. Quite possibly iTunes work very well on a Mac (I don't really care to be honest as I don't intend to use a Mac any time soon), but in my opinion iTunes and QuickTime for Windows are both really badly written. I remember a few years back when the free version of QuickTime couldn't play videos fullscreen. Maybe it's improved since then, but thankfully I've never had to use it since QuickTime Alternative was released. Actually last time I used iTunes on a Mac, one thing that really bugged me was that the maximise window icon would not actually make iTunes resize to the full screen, but rather would toggle between the regular iTunes windows, and a mini one. But this is not suprising considering how badly designed (in my opinion anyway) OS X is. Sorry to get off topic.
QT was definitely at the top of my list of intensely disliked multi-platform media apps, and I was quite happy to totally clean it off my system about a year ago. What the heck, these days there's lots of better apps can can handle QT media quite well. Probably my biggest gripe with it went back long before Windows, installing games which used (and included) QT for their videos. Far more often than not, they wouldn't properly check that QT was already installed, and never checked which version, so quite often it would simply over-write my QT with a much older version. Good riddance. And my apologies too, for contributing to temporarily side-tracking the main topic, couldn't resist the bait.
Used to be a JetAudio user but i had a couple performance issues with it playing HD movies in my laptop and i decided to change it for MPC-HC . . . What a difference. Now i'm a MPC-HC user!
VLC, sound quality blows in it though. owns for all the rest and can dubble as flash player if needed on some sties.
RealPlayer: http://www.real.com/resources/best-media-players-for-windows I was surprised not to see it mentioned above.
Zoom Player Pro. It just seems to play everything I throw at it, also it's fairly configurable and it loads so much faster than any other player I have used. I still use VLC from time to time but am always reminded of its slow loading every time I start it up.
WMP12 with K-Lite Codec Basic. Mainly because i like that the toolbars in WMP12 are all transparent, so even in windowed mode you don't loose real estate from the film. LAV for video, ffdshow for audio. Splash Pro as secondary (used to be my primary, but i found audio is worse).