I use a Yamaha StagePas 300 as described by Terry... a very convenient and compact little system. The mixer packs in the back of one speaker and the leads in the back of the other.

When I don't need that much I also use an Ashdown Engineering Acoustic Radiator 1 (100W) combo... very compact with a good sound and separate instrument and mike inputs, and a lot cheaper than the otherwise excellent AER combo.