The Crown and Anchor at Tropicana. I'm not from Vegas, but have been there during the last World Cup and also the 2004 Euros. GREAT place to watch the games. Good food, good drink, and friendly people who love soccer. Kinda bummed I won't be there until August. There's also a place called McFadden's (?) over across from the Orleans that's supposed to be pretty good as well. Good luck if you go to the sports books. I found them to be useless when it comes to showing the soccer games. Let us know how it goes!
Most Irish pubs in town will show soccer, though obviously they are tilted more towards the Irish teams. McMullan's is a great place, but isn't really suited to showing matches due to layout IMHO. Still great food. The Crown & Anchor seems to be the soccer bar everyone goes to. It's small, it's cramped, the parking sucks, and it could be considered a dive I suppose...but the fans come out. In 2002 they had set up big screen TV's so people could watch outside. There are usually at least 3 or 4 US fans there for most matches.
I will be in Vegas for the US vs Ghana game if you want to meet up and watch the game. Im willing to hang out with any bigsoccer members!