Only with careful searches can you uncover the very best bargains, as generally hotels would prefer folks to pay the "rack rate" or higher rates than the very best they'll be offering during specials.
Enter Twitter, which is often the source of great tips on bargains from individual hotels in Las Vegas. Here's a partial Las Vegas list on Twitter. Follow it for some information from Las Vegas folks and properties.
Also note that most of the Las Vegas hotels have Facebook pages and those will sometimes feature specials. Facebook and Twitter are a great way to get a fast response from many hotels as well.