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?