Need Help Implementing Location-Based Filters on a Used Car Sales Website

[codeanpeace]

What's the best way to do geo radius by distance search?

What would be the optimal way to have a set of locations in the database, and enable search of addresses by distance. i.e. All addresses within a 10 mile radius, etc I have the longitude and latitude of every address in the db. Is there a good dep for this, or is better to go the postgis route?