I keep a shot glass full of water in my desktop humidor for this very reason. I can't ever seem to get a grasp on keeping the humidity in check in that thing. I've tried beads, keeping the foam wet every week, etc.. its just dosn't like to stay steady. The shot glass helps.

I keep most of my cigars in a Coolidor these days. I don't seem to have the same issues I have with the desktop humidor.