I experience a fantastic trip to Las Vegas and highly recommend the Comedy Bus to Hoover Dam, the Bellagio Fountains, and the Fremont Street Experience. To my surprise Hoover Dam was actually the most enjoyable and the most fun. I have to give credit to our guide Jonie Maclain, she is a professional comedienne (the company she works for is called Comedy on Deck Tours) and very knowledgeable about the Dam; she calls herself a "dam encyclopedia". I laughed all the way to and from the dam. It's a great idea to put comedians on as guides and even better that they are so well trained (at least ours was).
In addition to Hoover Dam must see sites are the Bellagio Fountains (beautiful) and the Fremont Street Experience in old downtown.
The Bellagio Fountains are actually water canons and blast the water 400' into the air. It's even better because of the music Celine Dion, Frank Sinatra etc. If you are smart you will get reservations at Mon Ami Gabi, a restaurant across the street from the Bellagio. You can enjoy a delicious dinner outside on the terrace and see and hear the fountain show go off every 15 minutes, it was magical.
Fremont Street Experience: Every hour on the hour after dark all the casinos dim their lights and a light show goes off over you head on a canopy that is four blocks long. They turned downtown into a boardwalk so it is very eclectic, you can get everything from deep fried Twinkies to blueberry Margaritas, see street performers, and listen to live music.