I never used usb webcams with MAC until last week, I got Logitech C615 which is claimed MAC compatible (but most of the features dont work with MAC), there is sound issue when using FaceTime but it's perfect on Skype though. Try C910 or any of these should be fine http://www.mac-compatible-web-cam.com
BTW, this is repeated topic, Please search before posting, to reduce you carbon footprint