I used this thread
on Fat Wallet to book a stay at MGM for my trip next week. Don't be afraid to visit the casino's website to signup for their player's card first to get the better rate.
Cheapo Vegas can give some low roller tips also.
Something else to keep in mind, whatever rate you see on any site, ALWAYS book through the hotel asthey will usually match the rate. Just in case you need to cancel or change your reservation, you won't if you use the travel site.
Good luck....