Mobile Media Converter [Windows / Linux] is a great application which allows you, thanks to ffmpeg, to convert between a variety of formats including: MP3, WMA , Ogg, Wav, MPEG, AVI, WMV, FLV, 3GP video and AMR audio and even MP4 which is very useful if you have an iPhone / iPod.Apart from this you can download videos from Youtube easly thanks to its built-in download manager.
Overall, Mobile Media Converter is a very simply to use application which does not need you to write commands in a terminal, everything being made through a GUI.
If you use Ubuntu, there is a .DEB package which you can download. For Windows and other Linux distribution, download it from here.
Obviously, you need ffmpeg for this to work. For Ubuntu, see here for some fixed packages. Windows users only have to install the applications and it will work right out of the box.
