i've got the altec lansing inmotion speakers, and i must say they work quite well, they may not be the best, they're the only ones i've used so im not sure. but they are surprisingly loud and the sound quality is good. the only downside is that if you're running them off batteries (4 AA's) they dont last anywhere near 24 hours if the volume is turned up. so i wouldn't automatically go with my suggestion but you should look at them.
--andrzej