If the video/movie files you want to view are in a format that is not supported by QuickTime, we strongly recommend you use VLC Media Player. It is a free and open source cross-platform media player supporting most audio and video formats (H.264, Ogg, DivX, MKV, TS, MPEG-2, mp3, MPEG-4, aac, ...) from files, physical media (DVDs, VCD, Audio-CD), TV capture cards and many network streaming protocols.
QuickTime is a multimedia framework developed by Apple Inc., capable of handling various formats of digital video, media clips, sound, text, animation, music, and interactive panoramic images. It is available for Mac OS classic, Mac OS X and Microsoft Windows operating systems. QuickTime is integrated with Mac OS X, and it was an optional component at install for earlier versions of Mac OS. All Apple systems ship with QuickTime already installed. QuickTime for Windows systems is downloadable, either as a standalone installation or bundled with iTunes.
The QuickTime family of digital media creation, delivery and playback software lets you deliver live or pre-recorded video and audio to an audience of any size. When combined with QuickTime Player and QuickTime Pro, these applications work together to provide the industry’s first end-to-end, cross-platform, standards-based digital media delivery system.
QuickTime is available for Mac OS X and Windows operating systems, and is distributed free of charge. Some other free player applications that rely on the QuickTime framework provide features not available in the basic QuickTime Player. For example:
Any application can be written to access features provided by the QuickTime framework.
DVD Ripper for Mac is a professional DVD ripping software to get movies onto your Mac. You may use DVD Ripper for Mac to rip encrypted movie DVDs and remove copy preventions. It helps you rip and convert DVD content to any common video formats for playback with QuickTime on your computer.

(PC user? Get Windows version here)