If you looking for a truly pocket sized speaker, then this Mini Mini Speaker is the smallest we have seen for a while.
This tiny cube speaker comes in a variety of colors and you can connect it either via the fold away 1/8″ plug or via mini USB.
Available in Pink, Blue, Black, Orange, Green and White for $39.99 from Gizmine complete with cable and strap.
NB.. all orders from Gizmine for theses tiny cube speakers are shipped from Japan and all instructions are in Japanese. Who ever reads the instructions manual for anything though?