Turn an Altoids can into an outstanding headphones amp. Learn to solder by building yourself the most excellent Chu Moy headphone amp. It sounds great but cheap enough to give away as holiday stocking stuffers.
Headphone amplifiers might seem superfluous but when you step to some serious headphones you need more amps than most portable audio players can muster. If you consider yourself an audiophile and you're pretty handy with a soldering iron this is one project you need to do. Of course you'll need the schematics for one the best headphone amp designs out there the Chu Moy headphone amp.
Thankfully Tangentsoft.net has some incredibly detailed instructions for building the Chu Moy amp. Now one thing you'll need to be aware of are the OPA2134 OpAmps. There great but if want them you'll need to order them online at DigiKey and Mouser. For resistors, LEDs, and headphone jacks you can pick those up at Radio Shack.