The Tenth Doctor and Heather McCrimmon, for instance, visited Deep Ocean, a huge, Luxembourg-sized underground biosphere that had been constructed in the city. There, the duo encountered a Thalatth, a species capable of extraordinary metamorphosis. (COMIC: Hook, Line and Sinker)
The Eighth Doctor, Fitz and Anji met up with Iris Wildthyme in 1960s Vegas. Wildthyme also met Noel Coward here, and the Eighth Doctor, somewhat unusually, intentionally drank beer. (PROSE: Mad Dogs and Englishmen)
Real world location
Though it's possible that a real world location doesn't exist in the same geographic space in the Doctor Who universe, such cases are few and far between. Thus, the map at right is probably a good indicator of the DWU location of Las Vegas.