Your media player.

When it comes to video playback, Windows Media Classic is also interesting; it supports many different formats, including the modern MKV, and it recognizes subtitles and multiple audio tracks without any problems. I think it even supports DVD video, although I don't remember for sure.

I've been using it for a long time – it's easy to use and has good features. I installed the latest version of K-Lite Codec Pack – it plays everything I need :cool:
As for an audio player, I used to use Winamp, but I switched to AIMP about six months ago, and I'm not complaining :) I like the ability to open multiple playlists, the built-in tag editor and converter (which I think is better than Nero's), and a lot of other little things, like not having to click the mouse to switch between the main window and the playlist :D