I found out that the Helios One power plant actually exists (probably without Archimedes).
I also knew Nellis AFB, Hoover Dam and McCarran Airport were real, and some quick Googling showed that Boulder City also exists.
What other real-life buildings exist in the game world? Are the casinos based on real ones?
Best Answer
Here are places that exist in both the game and the real world:
The game also contains numerous locations that are parodies of real-world locations.
I'll start with casinos, since you asked about those specifically:
The Bison Steve casino is based on Buffalo Bill's Resort and Casino. Notable similarities include the large outdoor sign featuring a bison/buffalo and the presence of a roller coaster.
The Vikki & Vance casino corresponds to Whiskey Pete's Hotel and Casino. Vikki and Vance's "death car" and artifacts are on display in the Vikki & Vance's main hall, whereas Whiskey Pete's has an exhibit containing the car and clothing Bonnie and Clyde died in.
The Atomic Wrangler's exterior sign is topped by a neon cowboy who looks somewhat like the iconic Vegas Vic. The Wrangler moves one of his arms, much like Vic did before 1991.
The Silver Rush's sign looks a lot like the sign the Golden Nugget used in the middle of the 20th century.
The Lucky 38 casino bears a resemblance to the Stratosphere tower.
The Gomorrah is based upon the former Dunes Hotel & Casino, now replaced by the Bellagio. They share faux-Persian décor and theming, and have similar architecture. The Dunes was also the first hotel on the Strip to offer topless performances.
The remaining in-game casinos (The Tops and The Ultra-Luxe) do not seem to be based on real casinos.
And now for other locations:
Bitter Springs camp and Bitter Springs Recreational Area are located roughly along the path of the real-world Bitter Springs trail.
Camp Forlorn Hope is located at Forlorn Hope Spring.
Camp Guardian is located at Guardian Peak.
Camp McCarran is set up in the remains of McCarran International Airport.
Freeside is meant to be the remains of Fremont Street.
Helios One is a reimagining of The Solar Project.
The Ivanpah Race Track is based on an abandoned race track south of Primm. There's not much information about it online, apart from a few mentions in relation to the nearby Ivanpah Solar Power Facility, but it's visible on Google Maps.
Jacobstown comprises the remains of Mount Charleston Lodge.
The Jean Sky Diving shack is presumably located in the town of Jean.
The NCR Correctional Facility seems to be the now-closed Southern Nevada Correctional Center.
Novac's T-Rex, Dinky the Dinosaur, is a play on the Cabazon Dinosaurs, Dinny the Dinosaur and Mr. Rex.
The Southern Nevada Wind Farm may be a reference to the Searchlight Wind Farm, a wind power plant that was planned at the time of the game's release and has since received government approval.
The Welcome to Fabulous New Vegas sign is a modified version of the remains of the Welcome to Fabulous Las Vegas sign.
In the game, a monorail system connects Camp McCarran with the Strip. Las Vegas does have a small monorail system, but the portion of the monorail connecting the Strip to McCarran is only in the planning phase.
This list is incomplete. Anyone can edit it to add or correct stuff. To look for entries to add, go through the list of F:NV locations at the Fallout wiki. There should be a note if it's a real world location.