A lot of premium iPod cables i see for sale are simply mini-jack to mini-jack, but to take advantage of the iPod's superior line-out you need to make or buy yourself a cable, which uses Apple's dock-connector.

On deciding to go the diy route i sourced the dock connectors from Ridax, who sells all the variations and helpfully accepts PayPal for payments. For the cable itself, i originally used CAT5 which comes in stranded/solid flavours and is made from OFC copper, this proved a good cost vs performance compromise. If you're already into HiFi maybe you have some spare interconnects, good quality ones would make an excellent choice.