MAC Address Lookup Tool
This tool uses a copy of the Wireshark manufacturer database which is compiled from a variety of sources and is the most complete reference for MAC addresses that I have been able to find. This database includes the 24 bit vendor organisationally unique identifiers (OUI) as well as specifically reserved or commonly used MAC addresses such as Microsoft Loadbalancing, IPv6 multicast and HSRP broadcast.
Http iframes are not shown in https pages in many major browsers. Please read this post for details.