The only Wi-Fi I've run into in Vegas (I don't use it, but notice the offers) - Hard Rock & Wynn, with a fee of course. I seem to remember it in Luxor, too...

I'd try to search free Wi-Fi sites on the web, and then book a room somewhere right next to that source. I doubt hotels are going to offer free Wi-Fi, since they'll look at it as a revenue producer until major competitors start offering it for free.