The Vinyl District is a GPS-based record store locator app for iPhone and Android, and it's free. Currently US-centric, let's hope that evolves.
"Have a 5 hour layover in an unfamiliar city? Hit the “All Stores” icon for directions to the nearest indie shop and while away your time between flights digging through the crates. You can also check in and share your finds on Facebook, Twitter, and Foursquare.
Know of a store that’s just opened or just closed or just moved? Add or update that store’s status to the app..."