I second the renting a car thing. Boulder "city" is a fun place to visit... Hoover Dam is very impressive and I really liked the tour of it. Red Rock Canyon is just beautiful to drive through and get out and take pictures (also free I think?)
Bellagio fountains are fantastic... try to see a few of the shows as they rotate the songs (everything from modern to classical). The first time I ever saw them the song was Frank Sinatra's Luck Be A Lady ... a perfect vegas experience.
Also, not sure if you or your friends are into art but it might be worth checking out what Bellagio's Fine Gallery of Art seasonal installation is. A few years ago they had the Faberge eggs that almost never leave Moscow. Was quite an experience.
Venetian gondolas are cool... they have them inside and outside... I've done both... I don't really recommend one over the other.
Freemont Street Experience is so worth checking out.
Highly recommend the car thing... parking at all the hotels is free so it's a good way to get around especially if you have a navigator who easily picks up the main streets and freeway exits. (usually my job) Just avoid actually driving down the strip
