Alerts for new mac addresses

Is there a product available that will
a) allow me to build a database of known mac addresses and
b) alert me if a mac is discovered that is not in the database

I am not looking for a complete security package here, just an alerter to keep people from plugging stuff into my LAN. Of course if there is a better way to accomplish this I'd like to know about that too.

Thanks,

Sam Wheat