for converting audio/video files i recommend mediacoder. its a free and opensource project, and it can convert almost every format to all other formats available. In fact it is the most powerful media transcoder i have ever seen!

it can act as a Audio CD Ripper,

it can act as a DVD ripper,

it can be used as an iPod converter

it can be used to shrink DVD9s to normal DVDs

and much more...

it has a nice gui, but takes a while to get used, though after you get used, you will never use any other audio/video file converter.