Adium for that. But i use iChat becuase I only have AIM and gTalk accounts.
As for video since I have a Powerbook, I got iChatUSBCam (now iUSBCam) and a 20 dollar Logitech webcam for notebooks and it works flawlessly and is detected as an iSight. http://www.ecamm.com/mac/iusbcam/
I'm not sure if Pidgin has a Mac version or not, but that's what i use on my PC.