I've been here many times, mostly driving through on my way to Phoenix or back to Vegas. At times, the dam can be a hassle to drive over. To visit, however, it is a stop someone should be sure to take at least once in their life.
Parking is fairly easy to find at the dam but does cost $7.00. The tour we took was around $11 each and my 4-year-old was free (you'll want to check the website setup by the government for the dam for pricing and hours...also search for Hoover Dam Coupons, we saved a dollar off of each ticket). The tour takes you to one of the huge tunnels where water is pumped through and around the dam. The size of these tunnels are so big they could not be delivered and had to be built on site. Next they take you to the giant hallway where you can see the generators that have been in many a movie or tv show. Lastly you are taken back to the top of the dam for a better view of the front of the dam than you could get just walking around. You also can move to another building and see a movie about the dam as well as examine a 3-D map that shows the dam and where it came from and leads to throughout the West.
For those of you that just want to drive over the dam, you can do that...pretty soon there will be a bridge going over the mountainside above the dam that should relieve some of the traffic woes found in this area. If you've never visted the dam, you should do it at least one time. It can cost as little or as much as you can afford.