Are you playing with a band or just by yourself?
What's been working really well for me in the Ukulele Orchestra (following a recommendation on the subject by Howlin' Hobbit a while back) is a large diaphragm condenser mic (running through an ART mic pre-amp that I already had to provide the phantom power. Though most mixing boards should be have phantom power) I got a good ebay deal on a Joe Meek JM37dp package a while back that I really have no complaints about.
Since it's got a pretty wide pattern I can actually set it up about a foot and a half away and use it for voice, uke and pick up the harmony vocals that the person sitting next to me does. It does a really nice job and doesn't sound half bad for being a pretty cheap as far as condensers go.