If your visiting Las Vegas for the first time, i suggest taking a look at this site called www.lasvegaselitetours.com They provide all kinds of tour package for las vegas. They have great grand canyon packages, and also free comps for all kinds of casinos. Me and my mom took a trip to the Grand Canyon on a helicopter they provided. It was a memoral experience, its unbelievable how great the view is of the grand canyon from the sky. Take a look
Another Great Site!
My wife and I took a tour with Grand-Adventures.com and feel you probably won't find a better tour out of Las Vegas. Their URL is www.grand-adventures.com and their tours are all under $100 per person.
We are lifelong travelers and learned to search for niche and novel things to do when traveling. The big stuff is staple and we learned a long time ago that searching for the things to do that are a little harder to find more often then not turns up big treasures. We hit the jackpot here and have traveled to Zion, Bryce, Valley of Fire, and the Grand Canyon with them. They don't have ads for Zion, Bryce, or the Valley of Fire but will do them upon request. All of their tours are fully guided, they give you four hours at every park (trust me, even this is not enough time), give you an awesome, very professionally done CD of your tour, and give you a fantastic picnic while out walking around. Most groups are under ten people so check them out! The tour guides are also extremely fun too and always give you more then just the tour. They will stop anywhere you want and show you several additional sites along the way.