I've been really interested in geotagging my pictures so I recently picked up a couple of Eye-Fi cards. Basically, when I take a picture using my Canon 30D, the Eye-Fi card tags the picture with GPS information as to where the picture was taken.
Once you have a geotagged image it can be uploaded to Panoramio where the image can be superimposed on top of a map. Then, anyone searching for a particular monument or the like can easily pull up pictures taken in that location.
One of the goals I have is to document the area we'll be living in. There are a ton of pictures of the musée du Louvre and the other Parisian tourist attractions but very few where we are going to be situated and that's only a few steps away from the Louvre.
You can see what Panoramio has for our area of Paris by clicking here - remember, we are on rue Jean-Jacques Rousseau...