Las Vegas is also known as sin city: the town of gambling, partying, lots of lights, and smokey casinos. There are a lot of tourist attractions that you can definitely skip, but there are also a handful of attractions that you definitely do not want to miss for the sake of tourism.
Walking the Strip
Las Vegas is a dry desert city: in the summer it's extremely hot (a great place to get a tan) and in the winter it's extremely cold and even snows. However, it is always a good time to walk the strip from MGM all the way down to the Mirage to partake in all of the street festivities and interact with all of the interesting people. The best part of this is that in Las Vegas it is legal to drink on the strip which means you should get the large margarita with the whacky straw and go crazy.
This is the tallest coaster in the world. You have the option of taking the bungee-like coaster, or the circular coaster around the top of the tall building. It is kind of expensive, but definitely something that you should try when you go to Vegas.
Venetian Gondola Rides
Yes, this is also another tourism plug, but there's nothing more fun than getting on the gondola that goes down the Venetian casino Grand Canal and watching everyone gawk at you with your singing gondolier. The attention more than makes up for the money you will shell out for the ride through the casino.
Bellagio Synchronized Fountain
The fountain outside the Bellagio casino (also seen in Ocean's Eleven), performs a synchronized, colorful dance two times an hour (maybe even more in the busy season). The fountain is definitely something to see, but get their early and do your research. People tend to line up to see this fountain since it is one of Las Vegas' main tourist attractions.
New York, New York Rollercoaster
This rollercoaster is terrifyingly fantastic! It's a semi-hefty price, but the rollercoaster goes around the New York, New York casino "skyline" with terrifying turns and drops. The anticipation of the first drop makes the cost definitely worth it, and you won't be disappointed. Here you also want to do your research, because there is generally a long line for the rollercoaster (and they occasionally shut down for repairs).