Frappr

From frappr.com:

Frappr is an online tool that lets you map out the city where you live, work, vacation, or anything else! You can then share your unique URL with friends and find out where the rest of them live and work in relation to everyone else. It's great for keeping in touch with friends, families, and groups! You can also share photos, private message them, or leave comments on their MyFrappr homepage.