I've found a couple. One is 2.5D CAM, and another is SketchUcam-1_1e-beta4.
I have only tried SketchUcam-1_1e-beta4 so far. I got a SketchUp bug splat at one point, but had been playing around with it for a while and maybe I was doing something wrong.
Anyone try any of these or others and have any observations about any that work well?