Last time I was there - in 2006 - the best coffee was in my hotel room with a pour-over cone, a hand grinder, and beans I brought from home. I hope it has changed but would not bank on it. Starbucks was everywhere. I did try a double shot of espresso and a small gelato at the Illy shop in the Venetian. It's an "official" Illy shop. As Illy shots go it was pretty good and was far superior to anything else I came across in Vegas.
New York Central Coffee Roasters