I have been carrying AudioEngine speakers for a while now and I cant be more impressed with them as a top notch self powered small speaker. Just attach your imod or ipod and your groovin - no amplifier needed.
Plenty of reviews but here is a recent one.
Stereophile: Audioengine 2 powered loudspeaker
Again if your looking for a small speaker that will not kill your wallet but will be "killer" for sound, the A2 is the ticket.
ALOaudio - Audio Line Out: Interconnect cables and portable line out docks for iPod
Ken