XMI X-mini II Mini Speaker
I just bought one of these from Amazon and what a great little speaker it is. OK, I will not be putting my Logitech Pue-Fi Anywhere on eBay and the bass is as limited as you would expect for its size, but as a cheap speaker system for an MP3 player it is very good.
It is tiny, well designed and made, comes in its own little bag and has a cable with a 3.5mm jack built into the base. The sound is pretty good (within understandable limits) and it costs less than £20. If you want to listen to music when on the beach or on a picnic and don't want to lug around a larger dock unit, it is ideal. I will also find it useful if I am away with the family and the kids want to watch a movie on the netbook as it will go louder than the netbook will.
It is a mono speaker, but you can add others in a daisy chain to give greater volume. Please note, two speakers don't give you true stereo.