My nre mini-speaker works pretty well. Only complaint i have is that the speakers start to sound a little tinny right at the point where the volume is high enough so i can hear it easily while the car is going. That would probably be less of a problem if i could figure out some way to prop it up so it was facing me. The base is good enough for setting on a flat hard surface, but it doesn't do so well on a soft angled seat in a moving car.
I'd complain about the fact that it uses AAAs when it's large enough that it really ought to be able to fit AAs inside, but since i have the rechargeable AAAs now that doesn't matter so much.
Anyway, i just got to the second chapter in Speaker for the Dead when i got to work this morning, and i'm very happy thati can just play the audio books straight without having to burn them to CD first :)