Try the different travel sites like Orbitz and Expedia. Also, check out each casino's website. I prefer booking directly with the casino, but that's just me. Good luck and welcome to the VMB.
Try a host If you've stayed or played at a downtown venue, try contacting a host there. I stay at 4Q, and Paul Klocke always takes good care.
Have you tried the Las Vegas Advisor? If you become a member ($37 for the year), just a couple of those coupons will pay for the membership and then some. Check it out. http://www.lasvegasadvisor.com/
As mentioned above re:SWA, try booking a 'package' with whatever airline you're flying. Their downtown property packages are often very close to what you'll pay for airfare alone.
The package deals at SWA can be great. I got Rio for $25 a night in October. A few of the hotels were actually less than airfare alone, they are basically paying you to stay there. And that was for 5 nights. If you aren't flying SWA just do as suggested above, try all the travel sites, the hotel sites directly, call them, etc... I enjoy doing the research, others find it tedious