UMPlayer is a free and open source media player that comes packed with features.
The program is based around MPlayer, so you can be sure that it'll play just about everything: video and audio files (even if they're incomplete or damaged, in some cases), DVDs, audio CDs, SHOUTcast streams and more.
You don't have the video or audio clip you need? Not a problem, as UMPlayer has a YouTube search bar built-in. Enter a keyword or two, and a window opens where you can browse the results. Double-click your preferred option to start playing it, and click the Record button to download a local copy.
Convenient extras include the program's ability to remember its position in any given media file. If you had to stop a video at a particular point, for instance, just reopen it again later from the Recent Files list and UMPlayer will automatically resume where it left off.
You also get strong subtitles support, including the ability to search for subtitles at OpenSubtitles.org; there's an audio and video equaliser, screenshots and video thumbnail maker tools, and a host of configuration options that allow you to customise the program to suit your needs.