GOM Media Player might very well be the most hassle-free and full-featured freeware media player available. The player boasts several unique features--including support for a wide range of video file formats and built-in video and audio codecs that permit you to play video files encoded in the most popular formats without having to download additional files--as well as a codec finder that points you to download sites for the few encoding formats the program doesn't natively support.
The application also sports a patented ability to play corrupted, broken, or partially-downloaded video files, something that typically stymies most media player applications. You don't even have to wait to get the entire file to start watching: Even while you're still downloading a file, GOM Media Player can begin playback, so you don't miss a minute of the action.
With this impressive ease of use--and advanced features like support for several subtitling protocols used in digital video, settings to help you improve the playback quality of your files, and a built-in screen capturing utility--GOM could easily become your favorite media player.