Off the beaten path, this is defintely a Vegas must-see. As mentioned, tours must be set up in advance and cost a nominal fee, but well worth it.
A photographer's dream, the retired signs of old Vegas are arranged in two fenced yards. Our tour guide revealed some interesting tidbits in our hour-ish tour - if you are very familiar with Vegas you may glean a few little-known facts.
Otherwise, the Boneyard speaks for itself. Some of the signs are in varying stages of disrepair, which makes for many beautifully sad photo ops. As someone who isn't incredibly interested in picture-taking, even I found myself playing around with the various settings on my camera and different photographic angles.
In order to truly appreciate Vegas, visit the Boneyard and pay tribute to the past.