The Icom stuff is nice but I am a huge fan of Nokia HFS-12's. They are from older Nokia CARK-90 & 91 cellular handsfree kits. These speakers are incredibly loud and durable as well as compact. Their design is not visually obtrusive and they are smaller than the Icom speakers.
For whatever reason, (i suspect the cell phone application) their tonal quality sounds better to me than anything else I have found for scanner use. They have a very 'warm' sound to me.
They are generally less then $10 on eBay and often much less from other sources. They are getting harder to find as the kits they came from have been out of production for years now. I was never able to figure out who OEM'd them for Nokia despite trying.
Some are selling square replacement speakers. I don't know anything about those and suspect they are after market. The version of HFS-12 to have in my experience is rectangular with a horizontal grill design.
Here is one on eBay:
http://cgi.ebay.com/NOKIA-TYPE-HFS-12-E ... 286.c0.m14The Icom SP10 is essentially the same extension speaker Motorola sold for their Maxtrac/GM/CDM series mobiles. They are nice speakers although I prefer the Nokia.
http://cgi.ebay.com/NOKIA-TYPE-HFS-12-E ... 286.c0.m14My .00002 cents