I agree with 'Cat -- the Bellagio fountains are great. I'd rather watch the fountains again then ever go and see the "Sirens of TI".
Also, while you're there, make sure you go inside of the Bellagio and check out the conservatory (just keep walking straight forward as you walk in the main entrance). They change it up for each season, and it's always fantastic -- a great, free experience.
It's free to walk through the various new casinos, too, of course. If you haven't been to City Center, there's a fair amount to see in the Aria casino and the Crystals shopping mall. Cosmopolitan just opened, too, and I'm sure there's a lot to explore.
Also, while you're there, make sure you go inside of the Bellagio and check out the conservatory (just keep walking straight forward as you walk in the main entrance). They change it up for each season, and it's always fantastic -- a great, free experience.
It's free to walk through the various new casinos, too, of course. If you haven't been to City Center, there's a fair amount to see in the Aria casino and the Crystals shopping mall. Cosmopolitan just opened, too, and I'm sure there's a lot to explore.