What services can I used to find a user's location based on their IP address?

Question

If you need to locate a user based on their IP address, what services are available (free and not free services are fine)?

P.S. I understand that some users use prox

Answer 1

It's also worth noting that MaxMind allow you to download their geolocation database as a CSV file:

• http://www.maxmind.com/app/geolitecity