Just what it says on the tin - it's a free service with an API that does GeoIP lookups for you. 15k queries/hour before you get cut off. Returns results as JSON, CSV, or XML in addition to returning the external IP of whatever host you're using.
It’s always better to do things right the first time! So why not start with a scheme that can take you all the way from your small suburban office to an underground global headquarters where you torture British spies while patting a white fluffy cat. Start it off right and you never have to make significant changes to it again.
A website that can extract many different sorts of information pertaining to IP addresses and networks, least of all querying several dozen blacklists to see if an address has been flagged as a spammer's.