I lived in Vegas for four years and I believe I visited every gun store at least once. I've been out of town for about 10 months so things may have changed slightly but here's what I remember:
Which stores you go to will depend on what you're looking for. I'd recommend different stores is you just want to browse, if you want to buy ammo cheap, or rent a machine gun.
There are two "best" stores for everything. The first is Discount Firearms which is actually located in Henderson, Nv and is only a short drive away from the strip. I bought my AR there, they have a good stock, (plenty of evil black guns) and rent machine guns. Your other "best" store is the Nevada Pistol Academy(NPA). NPA was bought by FrontSight and it serves as their Vegas "gateway." THEY SELL GUNS AT COST, althought their stock isn't as great as others, and rent machine guns. You can also get information about FrontSight which is an excellent shooting school, less than an hour away from Vegas.
If you want to rent a machine gun and just fire a single magazine, Discount Firearms will be cheaper. If you plan on firing several magazines (or boxes of ammo) then its cheaper at NPA.
If you just want to browse and drool over cheap prices, Bill's Buy and Sell is the place to go. Bill's is a the major seller of LE weapons in the area as Metro encourages their officers to buy their own guns. He is the best Bushmaster LE dealer in the area as well. I would only go to the store in the bright hours of daylight as it is located in a somewhat seedy area.
Another good store to visit is National Survival Store. Its amazing how much stock these folks have crammed into such a small store but it is a lot. (It kinda fells like a Middle Eastern bizarre) They have great prices on ammo and their gun prices are reasonable. They have funky hours and are only open Thursday-Sunday if I recall correctly. Make sure you call before visiting.
If you want cheap ammo and to talk to a great guy, try Kent's Guns which is located on Water St in Henderson. Kent stocks a small selection of guns, and mainly sells clothing and ammo. He specializes in PMP ammo and always has good prices. (I've probably send several of his kids through college just by buying ammo.)
If you want gear, make sure you check out Fearless Freddy's. They stock a huge amount of gear - like BlackHawk and SureFire - you'll ever want.
You may also want to check out Machine Gun Kelly's over by the airport. It is more of a class III selling store if that type of thing interests you.
I don't remember its name but there is a gun store on the north side of town, I believe off of Cheyenne. You may want to browse as they have a good selection and generally have a good selection of pre-ban AW's for sale. I say "browse" because they are very expensive.
I would avoid The Gun Store on Tropicana. They rent machine guns, and sell guns and accessories. I have never had any good experiences with them and they charge high prices for everything. I would also avoid Craven's Gun Haven - he isn't the friendliest guy and his stock is lacking.
I have mixed feelings about American Shooter's Supply. They are a combo gun store/uniform seller. There selection of weapons is limited but they do have a range with rentals available. Their staff isn't the friendliest and I've never forgiven them for deciding to close the range early, about a half hour after my buddy and I got there and paid.
Be aware that Front Sight's Nevada Pistol Academy charges obscene prices for the use of its range. If you think $28 for a 50-box of UMC .45 ACP and $10 for a range fee is reasonable, then by all means visit them. NPA will NOT let you use your own ammunition. In contrast, both Discount Firearms and The Gun Store charge only $5 as a range fee and The Gun Store has a larger full-auto selection than NPA. Either one allows you to bring in WalMart or other reasonably priced ammo. Another place to check out is American Shooters Supply. They have a wide selection of handguns as well as full-auto guns in addition to a 50 yard range in the $7-8 range.
I have had the opposite experience with The Gun Store that ajp3jeh described. They and Discount Firearms are the LOWEST priced stores in town, American Shooters Supply and NPA have the highest prices in town. Believe me, with the last 6 guns I bought American Shooters Supply ALWAYS had the highest prices.
Bill's Buy & Sell is a fine store with lots of reloading supplies.
Enjoy your visit to Las Vegas!!
Discount Firearms is a fun range with rental guns exceeding other states total for sale guns. Mostly Glock but you can rent a tommy gun w/ full auto. For a blast from the 20s-40s full auto past. For $20 dollars for a 30 round mag. I have just retrained for indoor shooting again yawn! But just traded off my freedom providing 4X4 Nissan. Which could get me so outdoors I had to search for signs of civilization. Which I miss, but indoor yawning is best at Discount in my opinion.
I have heard alot of people complain about the Gun Store.Personally I like the guys over there..they know their stuff . Plus the have one of the best CCW and rangemasters in town. Discount Firearms is another good place..we used to have some great pinshoots there . I gotta convince Johnny into starting them up again.
While you are in the area of discount you can check out Spurlocks Gun Shop on Basic off Boulder Highway ( about 3 miles South of discount ) and further up Boulder another 3 miles or so is a new gun shop. I forget the name but stop by and say hi to Leon .
If you are looking for a holster...Cravens is the place to go look...he has a huge holster selection...a bit pricey but he has alot. Bills buy and sell has prices comparable to discount but they are in the downtown area off of maryland and Fremont .
I usually make a round trip...start at the Gun Store on trop...go east on Trop to boulder...right onto Boulder...on the left side will be Accuracy Gun shop....about 8 miles South on Boulder and you hit Discount Firearms....up boulder South to Water Street..bare right....about 1 1/2 mile on the right is Kents Guns....head South up Water to Basic & hang a left on basic ( 7-11 on the corner ) and down there about a few blocks on your right is Spurlocks.....then
head East on Basic to Boulder...hang a right....head up Boulder Highway about 4 miles or so on your left will be a Gun Shop ( cant remember the name..Leon just opened up a few months ago ).
If you are in town for the 2nd Sunday of the month...trek on out to Desert Sportsman and check out the SubMachinegun Shoot .
IPSC, IPDA and Cowboy shooting out there as well on certain weekends . Enjoy your stay in Vegas ( whatever you do DO NOT BUY the 50 cal Barrett at Discount Firearms..IT'S MINE !)