The Neon Museum (also often referred to as the Neon Boneyard) is, as they will constantly point out to you on their site and in person, a non-profit organization dedicated to collecting and exhibiting some of the historically-relevant neon signs from Vegas' past, which is constantly growing as classic casinos reach their end and are demolished for new resorts. They have signs dating back to the very beginnings of Las Vegas.
If you're a fan of Vegas, it's a definitely must-see, but it also makes for an incredible place to take some really unique wedding and engagement photos. The last time I was there (summer 2012) they required that you book in advance for tours, which are $15, but if you want to have an actual private photo session there, they base the price on how many people will be in your party and the number of photographers.
As of December 2012, their new building is now open for private events. They have a few options:
There is a $1000 security deposit required. There is a $35/hour security guard requirement for all events. A valet parking requirement is in place for events with 51 or more guests; pricing is separate. Finally, there is an option to add on $200/hour private guided tours of the full boneyard during the course of your event.
I'm not sure what the pricing is if you want to just have a private photo session in the boneyard. In summer 2012 normal tours were on hold while they finished construction on their new building but you could still do the private sessions. In June of 2012, my wife and I did a photo session there which was $300 for one hour with the two of us and a 2-person photography company (Mike L Photography) in the last slot of the day which was 7pm to 8pm. Not sure if the price varies by month, time of day, etc.
Their website is http://www.neonmuseum.org/
There are two different addresses I've used for them; their normal street address is:
770 Las Vegas Blvd North, Las Vegas, NV 89101
A second address you may need if you're doing a private session in the boneyard is: