The best site for Vegas, which checks ALL properties and gives rates per night for your dates, is:
www.hoteldiscount.comThis site goes by many names: 180096HOTEL.com, hoteldiscount.com, hotelreservations.com. They all take you to the same site.
When making your reservation, you will need to pay in full up front. There is a fee for cancellation (either $25 or $50, can't remember), but worth it to me for the deeply discounted rates that I have found. Call the hotel direct first to get their best rate. ALso, look up rates and specials on their own hotel web site. Sometimes you can find online specials on their own site. And add yourself to their e-mail list if they have one. One note, if you call the particular hotel that you want to stay in and tell them that the hoteldiscount.com web site is offering a lower price, don't expect them to match it. I have not had luck with that attempt.
In addition, be sure to check if the discount site is offering a rebate during your month of making the reservation. Usually, they offer a mail-in rebate of around $5 or $10 per night. Three nights can add up to a nice rebate. No strings attached! You just mail in the form after staying, and a check comes in the mail in 3 weeks.
We have been pleased with the rooms reserved in the past this way. Good Luck!