Las Vegas: Mob Museum
If you're going to the Neon Museum (which, to me, is first priority) then you might as well get the combo ticket to the Mob Museum.
Honestly, this museum could take you all day. And it's got every museum exhibit feature design that you could possibly think of to keep you intrigued and entertained throughout each part of the exhibit. I was taking an Experience Design class at the time, so I was paying particular attention to the way the exhibits were designed, and I was extremely impressed.
But other than the actual exhibition design, the information about the mob blew my mind (blowing minds — a mob trademark). The mob was everywhere. Maybe, probably, still is.
Just be careful you don't get caught being associated with the mob like we did (above). At least these are the friends that would be in jail with me instead of just bailing me out ;)