If you want to play video or music files in just about any format, VLC media player is probably your answer. 

Features
Usability
Conclusion
What's new
VLC media player supports the following formats

Version 2 ("Twoflower") brings a new interface, faster decoding, support for more formats and the ability to play HD and BluRay. It still remains however the most stable, flexible and lightweight audio and video player around today. While other media players will play unusual formats after downloading a codec, or simply refuse to play things,

VLC media player handles tons of formats, from MPEG to FLV andRMBV files. Version 2 has seen some important additions too such as support for 10 bit codes plus multi-threaded decoding for H.264, MPEG-4/Xvid and WebM.

Also useful is the fact that you can use VLC media player to preview files you are downloading since it plays incomplete parts of video files. VLC media player is not just for video playback however. It also offers superb integration with video channel streaming services such as Channels.com giving you access to channels such as ESPN, Reuters and National Geographic. Just right-click or CMD-click on the playlist, select Services Discovery and Channels.com.

Channels.com will then appear in your VLC media player playlist. Click on it to reveal the the different categories of channels available. Click on the category you want and a drop down list of all available channels appears in VLC media player. Just click on the channel you want to watch and streaming should begin almost immediately. 

VLC media player also has great hotkey support and if you take the time to learn the shortcuts so it can be controlled without touching your mouse. If you're watching DVDs or video files through it, this is not an issue. For music, it plays more or less any file and features an equalizer and playlist creation. VLC media player isn't as intuitive as iTunes as a media manager, but it's a much more flexible player in terms of file formats. You can even use VLC to convert your files, and on top of all the formats and physical media it will play, many streaming protocols and TV capture cards are supported.

VLC media player makes it easy to add subtitles to your video files too - just add the SRT file to the folder where your video is kept, and it will automatically play with subtitles.

Finally, the interface in VLC media player has been somewhat improved in version 2 although it remains strictly functional. However, you can download skins to completely change VLC media player's appearance. The preferences menu is comprehensive without being overwhelming, and there is extensive documentation online. 

VLC Media Player is quite simply the best multimedia application for Windows and Mac. It plays just about anything, hassle free - what more could you need? 

Rework and fixes of the Mac OS X interface

Fix Pulseaudio initial synchronization

Fix MKV, SWF, AIFF and subtitles demuxer crashes

Translations updates and new Welsh translation

DVB-S delivery system detection

Fix audio and video track selection through libVLC

Fix system sleep issue on Mac OS X 10.5