I tried a lot of virtual webcams. I think I can share my points on this topic.
Splitcam: free, but it contains toolbar/adware. User mode simulation.
Fake Webcam: too simple, only has the simulation feature, can not read your physical webcam. User mode simulation.
WebCam Simulator: Also only has the simulation feature and it seems the developer has stopped upgrading.
SuperWebcam: Doesn't work on Vista/Windows 7.
WebCamStudio: java based, gnu, linux, wow...