Get a Vox DA5, Faricelli. It's a very versatile amp with a lot of inputs and outputs. It has a seperate jack and volume control for a microphone. You can plug three things at a time into it:
1. Your uke - it has 11 built in adjustable effects models
2. A microphone - It takes a 1/4" (like a guitar cable) plug and has it's own volume control on the back to adjust it seperately.
3. A CD or MP3 player
What this means is you can plug in a CD/MP3 player, play your uke along with it and sing along with it all at the same time!
The Vox DA5 is also very light weight - about 8 pounds. I've carried mine in my luggage on the airlines, where you have to be carefull about the weight limit.
It runs on AC with the included adaptor. It will also run full power for almost 20 hours on a set of batteries, so you can take it anywhere. I've used mine for busking at the beach. Ric