Las Vegas, as one of the world's top travel destinations, has more websites devoted to it than you can shake a pair of dice at.
I'm still not clear why "Vegas.com" claims to be the 'official' site when VisitLasVegas.com appears to be "the" official site of the tourism bureau, but when booking you'll want to check rates at several sites and generally you'll be better off starting with Kayak.com for comparison shopping on prices. Then contact the hotels and other consolidators to see if you can land any special deals.
Here are some sites associated with Vegas.com:
Celebrity Week In Business Las Vegas Life Las Vegas SUN Las Vegas Weekly LasVegas.com Ralston/FlashLas Vegas Magazine Vegas Golfer VEGAS Magazine