Just one small point. Depending really on the quality you are looking for.

If this is for live work, then the quality of MP3 as stored on the iPod is not an issue, and the comment regarding 3.5mm jack to whatever your mixer can take, phonos etc is fine. Watch for earth loop hum from some cables though. If you do get a buzz, try removing the earth tag on one end, (easiest at the jack end if it is not a moulded plug) as this can sometimes alleviate the problem. Some leads do, some don't and the price / quality is not a real indicator.

If you are looking at studio work, using the iPod as a convenient store of music tracks, (especially in a higher supported format,) then consider taking the signal out of the iPod digitally via the USB to a half decent DAC (digital to analogue converter) of which most makes and models have phono output.

I find a small iPod, with it's solid state memory to be a robust piece of kit for storing tracks, and away from the well advertised uses, really does take it's place in the PA and indeed small / home studio application. (Ditto many other makes, and the inbuilt DAC being the only real quality comparison.)