The November issue of the magazine, Acoustic Guitar, has a feature called "Plugging In" with recommendations for small amps, DI boxes and effect pedals. The five compact amps they review and recomend are, Fender Acoustasonic 150, Dean Markey Ultrasound, Fisman Loudbox Artist, AER Compact 60/3 and, Roland AC-40. I would suggest searching the many acoustic guitar forums - there are many very good ones - where it is possible to find a great deal of info and experiences with small amps that is directly revelant to ukulele players.