Tracking down the vendor portion of a MAC address

I was trying to track down the source of an IP address conflict earlier today and I came across two sites offering a search service for the initial 24-bit (6 digit hexadecimal) vendor portion of an Ethernet media access control (MAC) address. The IEEE service is the official one, from where you can also download the complete listing, but MAC finder is also useful as you can use the ?string=00%3a00%3a00 command on the end of the URL (replacing the zeros with the appropriate hexadecimal digits).