Hi
This is a very useful thread.
I've looked through it and haven't seen a specific recommendation for an audio and video file converter.
So I'm suggesting
WinFF.
It's based on a program called ffmpeg, a fast converter used with Linux which converts (almost) anything to anything.
WinFF is ffmpeg with a GUI. There's versions for Windows (95-Vista) and also Linux.
The program has several 'pre-sets' for commonly used jobs. You can tweak them or create new ones if you like.
It's a free download from Bigg Matt's website. Here:-
http://biggmatt.com/