MAC address assignments

Folks, Where can I find a list of MAC (ethernet) address assignments. i.e. blocks of addresses were assigned to various companies. for example 8:0:20:xx:xx:xx is most likely a Sun machine 00:c0:7b:xx:xx:xx is some form of ascend router. I'm trying to track down someone who is using an IP address that they should not be using and all I have is their MAC address (00:20:af:f2:2c:79) I can take my answer off line geoffw