If you are thrill seekers, ride the rollercoasters at NY, NY and Paris. Also, ride the freefall ride at Paris. For looking, Bellagio fountains were really neat. The Freemont street experience is also a really cool site as is the pirate battle at Treasure Island. Don't forget to ride one of the 3 monorails along the strip. One of them takes you from the Monte Carlo to the Bellagio.
If you want to window shop, I would suggest the Venetian. They have St. Marks square where there are many stores and eateries. They have gondola rides (like in Venice) along with wandering musicians and even some living statues. Don't just hit the large popular casinos, look for a few of the small, out of the way ones. I found a casino that had 25 cent craps and 50 cent blackjack. Not the most plush casinos but your money can get stretched a long way while still having fun.
Hope you have a great trip.
Adam aka Big Dude