There are not too many museums in Las Vegas, but you might find some of them interesting to attend:
The Mob Museum - learn the Las Vegas mob story, find out the names behind organized crime, see interactive presentations and unique artifacts. Tickets are just $20, can be purchased online or at the museum. Located in Downtown Las Vegas.
Neon Lights Museum - the city that never turns the lights off should have the neon lights museum. Visit it to learn about iconic Las Vegas sights. Located in Downtown Las Vegas. Guided tours are available daily. Book online at the museum's website.
Natural History Museum - if you are in Las Vegas with kids, it might be a good idea to visit The Natural History Museum of Las Vegas. The list of exhibitions, hours and information about admissions is at the museum's website.