Windows: The Windows Media playback field is a crowded one, and it's tough to find a tool that can handle multiple playback formats. SPlayer is a gem of an app that manages just about everything audio and video.
SPlayer gets the job done thanks to binary codecs, and even plays Blu-Ray and DVDs. It has most of the bells and whistles you'd expect to find in a media player, including fullscreen mode, basic audio controllers, continuous playback options, and subtitles. SPlayer even sports a screengrab button so you can capture still shots from video.
One of the only drawbacks to SPlayer is that its web site is in Chinese, but it's easily translated via Google Translate. The app's controls and user interface, however, are available in English. If you're looking for something with a different interface, and maybe some unique features, over house favourite VLC Media Player, SPlayer is a free, open source download that runs on Windows 7, Vista, and XP.