SMPlayer is a free multimedia player for Windows and Linux with built-in codecs that can play virtually all video and audio formats. It doesn't need any external codecs. Just install SMPlayer and you'll be able to play all formats without the hassle to find and install codec packs.
One of the most interesting features of SMPlayer: it remembers the settings of all files you play. So you start to watch a movie but you have to leave. don't worry, when you open that movie again it will be resumed at the same point you left it, and with the same settings: audio track, subtitles, volume.
SMPlayer can also play videos from YouTube and other sites. Other features: Automatically find and download subtitles. Thumbnail generator. Many audio and video filters. Skins. Available in more than 30 languages.