most people for these small devices use active speakers (basically small speakers with a built in amplifier ) these are powered by battery or mains power and run quite happily from the headphone jack.nearly all music hardware stores sell them or can buy them for next to nothing from www.ebay.com. i use my basic surround sound speakers from an old pc on my mp3 when im at the bottom of the garden in my workshop,works great,but as you want portable i would go with the battery option they are small and light enough to take out with you.