Is there a bluetooth camera that works with an iMac?
What exactly are looking for? A Security Camera? Take a look at BestBuy's, Amazon or the AppleStores camera section. Most USB, Bluetooth or Ethernet cameras should be supported out-of-the-box.

Here are some ideas:

Withings Home HD WLAN  Video Camera



Arlo Netgear Wire-Free



NetCam Wi-Fi Camera with Night Vision