…ok, so you want a killer web app that will locate the position of the current visitor? No problem. Here are the tools of the trade. (Your requirements may vary, for me, i want Lat/Long information, with regards to the KISS principle)
1. IP to location databases
Typical providers include ip2location, ipligence, maxmind. They are usually expensive, static, and just too big. The concept is that you have a big database downloaded and monthly updated, and you can open that database to get the location info from whatever platform you want.