The travel section on Thrillist puts it succinctly:
Everybody wants free stuff -- especially in Las Vegas. Regrettably, the days of wildly cheap buffets and gratuitous drinks at casinos are pretty much long gone. But here's the good news: There's still a little bit of free fun to be had in Las Vegas. You just gotta know where to look.
You'll also find a wealth of links and travel tips in their Ultimate Las Vegas Travel Guide.