The Panasonic SP100 falls into the category of small portable iPod sound dock. It's the best I've heard in it's price range, with only the Sony SRSGU10IP coming close - and that's quite a bit bigger.
I'll start with the only bad point - it doesn't have any extra features. No radio, no clock, nothing. If you can't live without that, then don't buy this.
However, if you don't want an FM player, or a clock (the iPod has one anyway), then this is a great choice. I compared several other products with this side by side and it came out on top for sound quality for its size by a mile.
The units I compared it to were:
Sony SRSGU10IP - the Sony is much larger, but of similar sound quality. A good alternative.
Altec Lansing inMotion IMT702 - this unit didn't even come close with the sound reproduction.
Altec Lansing IMT 620 - slightly better than the IMT702, but had no depth of bass and a very artificial treble sound.
JBL Micro Radial Speaker with iPod Dock - good volume but hardly any bass and the circular speaker doesn't give a good directional sound.
PHILIPS DS8500/05 Fidelio - Low quality and expensive, similar treble but lacking much bass.
The only unit to come close for bass and treble was the Sony one. Nothing else was even close, which made my choice so much easier. The enclosure with passive radiators effectively doubles the bass output. I've had passive radiators in my car stereo and they work by enhancing bass in a small enclosure. The effect is that you can get away with a small sized unit with the bass of a much bigger competitor. Quality is very good, it's very easy to use, and has a handy remote.
I like the fact the unit holds the iPod properly with a back support too. Lots of the others don't, and it makes me feel like I'm going to break the unit if I press too hard on the iPod.
Without a doubt, this is a great product!