Maxmind is a cool company that offers location services for a small monthly fee. In addition, they offer a subset of the databases their services use to the public under an Open Source creative commons attribution licenses. If you download and load one of these databases, you’ll be able to do IP to location lookups. Cool stuff!
For Bridal App, the platform for the bridal industry that I’ve been working on, we want to show the visitor those bridal dresses that are actually available in their area. For highly detailed location data (provided by the W3C Geolocation Api) we need to ask the user’s permission, but we can get a rough estimate of where the visitor is based on their IP address so we can start out at least somewhere in the right area.