What are you interested in? Clubbing/dancing? Spa? Just sightseeing?
My favorite thing to do in Vegas is just walk around and check out all the different hotels. I think the Wynn and Bellagio are really beautiful. The Bellagio has this magnificent courtyard display of botanicals (maybe that is not a word, since it was just underlined in red) and decorations that is a tourist attraction in itself. I like going to downtown Vegas to get that true, old school Vegas experience (I do prefer to gamble down there, but know that is not part of your itinerary). You can also buy discounted show tickets on the main drag down there, but don't think they have any Cirque du Soleil.
As for buffets, the one at Mandalay is nice but expensive. Paris is also pretty good. Many of your big city's well known restaurants also have a outpost in Vegas. I'd skip Tao, way overrated IMO.
Audrey - Feb 2010
Anderson - Dec 2011
Please, no babies in 2012!