Hilton Grand Vacations Club (on the strip across from Sahara) has free wired broadband in all guest rooms, and free wifi in the lobby / common areas.
McCarran airport has free wifi in the terminals.
According to ads on the monorail, the Nextel store at the convention center also offers free wifi.
There are quite a few starbucks outlets that offer t-mobile hotspot ($10/day or $30/month).