Some things that we found fun on different trips to Vegas are:
Take a helicopter flight over the city - daytime or night time are both good.
Eat at The Steakhouse (inside Circus Circus) - a real surprise, a bit of "old Vegas" and really, really great food and atmosphere.
Check out the Mob Experiance at the Tropicana - interesting (and you can also see how they are "updating" the Trop without tearing down an old casino and building new).
Go on the zip line on Fremont Street downtown (and also check out the night time light shows) Get your picture taken with a million dollars at Binion's and also enjoy the Shrimp Cocktail at the Golden Gate - where it all started!
Definately watch (and listen) to Belligio's fountain shows - if you can get at table at Bon'Ami (Paris Casino Resturant) at night it is very pretty and relaxing, if you eat there during the day - it is great people watching.
If you like to see the old neon signs you could go on the Boneyard Tour - check ahead for the hours of the tour - they seem to change times alot.
See lots of shows, there are all types of shows ranging from free to expensive so you can definately find some that you like.
Also get slot cards from the casinos you go thru, lots of times you get free small gifts or play time and then there is a good chance that you will get offers from them later on. Go thru the casinos (old and new)and check out the different designs and themes of them all. Also check out the new City Center with the fountains and art. Take the trams between some of the casinos (Belligo/Ari/City Center, Excalibur/Luxor)
Go check out the Atomic Testing Museum and if you have time take the tour to the Nevada Test Site (by bus, on the outskirts of Vegas). Or head out of town to the Grand Canyon (esp. the Skywalk), Hoover Dam, Red Rock Canyon or just for a drive.
Just some ideas, if you mention what you are interested in I bet everyone will have lots of other hints and ideas for you.