Cirque du soliel, in this order...: Mystere, O, Love, KA Zumanity. And yes, the tickets are worth it and you will both enjoy them. If you have never seen one, this is a must!!! Get tickets on-line ASAP.
Celine Deon was OK, but only for free.
Penn & Teller show!!!!
Watch the Belagio fountains from the bar that overlooks them. Can't remember the name.
Roller coasters: New York New York = Good. Desperado out in Prim = very good. The others are OK at best. Stratosphere rides if you just want to be scared.
See how many unique insults you came come up with for the people handing out porn on the corners.
Hang out at the pool.
Forum shops (Atlantis show is pretty cool/hot) You will score bonus points. Outlet shops are pretty good also.
FRY'S!!!!
Sirens of TI show outside treasure island. Volcano in front of the mirage.
Food:
Samba Brazilian Steakhouse @ Mirage!!!! Don't eat lunch!!!
Voodoo Cafe @ Rio
Anything at Caesars
Bars: Ghost bar @ Palms, Voodoo Lounge @ Rio
Indoor sky diving
Freemont street experience at night downtown.
Walk the strip and check out all the casinos.
Monorail is a waste, don't bother unless you use it to get back from your strip walk.
Helicopter or blimp ride...
Hoover dam
That's a good quick list.