Forget spending money on a Vegas show. You can see all the Vegas splendor you want, for free. In addition, there are many "shows" that happen at the hotels that don't cost you a penny.
For example, there's the volcano at the Mirage hotel. Every half hour, the volcano "erupts". First, you hear the rumbling. Then, you see the smoke billowing from the top of the mountain. Slowly, the orange "lava" starts to flow over the side, followed by spurts of fire and lava plumes. By the end of the show, the area around the base of the volcano is on fire, and the heat barrages your face.
My favorite show was probably the dancing fountains at the Bellagio. The water shoots "dance" to the music, following patterns and rhythms. Very elegant, and it could be very romantic if you're there with your significant other.
Then, there's the Treasure Island show. Gotta say, I wasn't impressed. There's a pirate battle, and one of the ships actually sink. You can't really hear what's being said, and people falling off the ship one after another can only go so far. But it's free entertainment.
Inside of Mandalay Bay, there is a beautiful botanical garden to behold. When I went, it was Chinese New Year, and the flowers were arranged into the shape of a beautiful orange and yellow dragon.
The Stratosphere, while at the end of the "old" strip, is a must see -- if only for the view. Just stand on the observation deck and take a look at the lights of Vegas, and contemplate the amount of electricity it takes to run the place. If you can stomach it, ride the Big Shot. Which is a tower that sits on top of the hotel - the second tallest building in the US. You strap yourself in, and then like a reverse bungee, you're "shot" into the air. That was a little much for me, but I did ride the roller coaster that also sits atop the hotel, and it was a fun time. You dip, and see nothing but the ground below.
If you like roller coasters, New York, NY also has a coaster. The cars are made up to look like a NY cab. You can take a dizzying look at the faux New York Skyline.
And who can walk by the Eiffel Tower replica in the Paris hotel and not want to ride to the top? Not to mention the photo ops.
And that's just naming a few. Each hotel has it's own gimmick, and each has it's own appeal.