If you have a newer Mac you have the built in iSight, but you may not know you are still missing out on taking your mac's vision to a new level. I've personally used both iSight's and the difference is clear.
Although the iSight doesn't come with adjustable options, software from companies such as
iGlasses can give you the flexibility you need to make a powerful combination of video capability and software flexibility on your Mac.
At $149, the iSight is not for the faint of wallet, but let's be realistic..... this is Mac hardware.
I've given my experience with iSight a 4 star rating. Great performance, and very useable in various situations with iGlasses add on software.
You can read the 4 star review Cnet did on the iSight here:
Apple iSight WebCam reviews - CNET Reviews