We went to see The Hoover Dam. It's only about 30 min drive from The Strip. Parking is $7 Cash only.
Paid for the $30 Dam Tour per person - charge it. You can see the Visitor Center, Powerplant, & Passageways within the dam itself. Don't go the Day after Xmas which we did - busiest day of the year the lady told me - just too many people.
It was ok. Visitor Center was ok; Powerplant - you get to ride the elevators to the bottom & see some stuff, generators, look out a window in the middle of the dam. Then go up to the top of the dam - I saw cars drive on top of it too so probably can do it free, not sure.
There's a store to buy stuff & cafe to eat stuff next to the parking lot. Didn't buy anything at either place.
We then went to walk on the new Mike O'Callaghan-Pat Tillman Memorial Bridge that opened Oct 20, 2010. You can see it from The Hoover Dam, then later drive back on the road & walk on the bridge. http://www.hooverdambypass.org/
We did see parking on the Arizona side, I think it's FREE, but then you gotta walk a ways to the visitor center, but if you just want to take pics from the dam, might be worth it.
Gotta see it at least once.