We took a half-day trip to Hoover Dam (with a stop at Lake Mead) with Vision Tours. Rather than dealing with a rental car in Vegas, we decided to let them lead the way.
The shuttle bus picked us up in the morning right from our hotel and took us to the "processing center." Once we got on our specified bus, we were to the Hoover Dam in no time. The bus driver was a riot; she kept most of us laughing the entire drive.
Hoover Dam was a site to see. Even though it was a million degrees outside (dry heat or not, it was hot!), we enjoyed a couple of hours of exploring the dam. It's unfortunate that you can no longer go deeper into the structure, but they did have some great exhibits and information. The memorials to the men who fell while building the dam were moving. This site is definitely a must-see.
After the dam, our bus driver stopped at Lake Mead for about 5 minutes so that we could get out and take pictures. It was a beautiful lake.
All in all, the trip was a success. Vision did a really great job, and we felt it was a good bargain for what we got.