Smallest Bookshelf Speaker Worth Listening To

I second System audio & LS3/5A. The size of S-Audio is inversely proportional to the size of the amp that will drive them to perfection. The cost is comparable! They're supposed to be mega-speakers for a small room -- the idea being that a small room can acommodate the appropriate amplifier...
Audio Physic Steps are also nice, & the Triangle & JMR are pleasant performers for a VERY pleasant price, IMO.

Sequerra Payramid MET-7 ($1,100) link:
http://www.sequerra.com/prosound/data/index.html

Totem Acustics Tabu are wonderful for jazz and classical.

GR Research Paradox 1

Acoustic Energy Aegis 3 speaker active speaker system are 4-6" high. Don't know if these were mentioned above.