Hello
I have been using Media Player Classic for some time now (looks like ms windows older media player. It is simple; FREE; It has very usable keyboard functionality and the slow / fast motion & frame by frame keyboard shortcuts & buttons actually work. It plays almost everything w/ the right codec’s.

DivX Codec is a very important, it utilizes all the latest tech (HT dual core etc.) and is well known for nearly doubling a pc’s quality output& it’s free. Windows Media Player 10, fully upgraded is a necessary evil because it shares most of its abilities with other player formats and the latest / newest technologies (& their codec’s) are usually made available to Windows before anyone else so occasionally it is the only thing that will work.

Lastly to complete the formula, including .mov .asx .asf and MORE the creators of Mplayerc released QuickTime Alternative; a newer version of Media Player Classic that plays...well…here is an excerpt from the Installation agreement information:

Media Player Classic [version 6.4.9.0]
This is a full-featured player which has internal decoding support for DVD, MPEG-1/2, MP3, MP2, AAC, AC3 and DTS. It also has internal support for opening MP4, Matroska and Ogg containers. Media Player Classic is also capable of playing QuickTime and RealMedia content if those codecs are installed.

QuickTime codecs [version 7.1.0.210]
Required for playing QuickTime content.
QuickTime plugin for Internet Explorer
Allows you to view QuickTime content that is embedded in a webpage. This is installed together with the QuickTime codecs.
QuickTime plugin for Firefox/Mozilla/Netscape/Opera
Allows you to view QuickTime content that is embedded in a webpage.
Extra QuickTime plugins
Some additional plugins.
QuickTime DirectShow parser
Allows you to play QuickTime content in all DirectShow enabled players. This filter works with most files, but not all files. It is therefore recommended to use Media Player Classic to play QuickTime files.

This is my best recommendation & should handle just about everything.
I hope this helps
GOOD LUCK