We went March of last year and stayed at Treasure Island. We just booked through the hotel website and got a great deal. I don't know if it was the best deal but it worked for us.
Try www.smartervegas.com. They usually have a list of all current promos the hotels are offering. Also, if you sign up with them (free), you can see their "secret deals," which can be a bit better. I did see some REALLY cheap Vegas rooms on the Expedia UK website if your credit card doesn't charge foreign transaction fees.