Vegas food, like the city, spans everything from cheap eats to mortgage payment meals, but the variety of gluten free options is more limited. My wife has coeliac disease (gluten allergy) and the following are the places we ate at (without symptoms) during a 3 day September 2013 stay:
Wynn buffet for breakfast is the best bet if you need (or want) to have a gluten free version of the extravagant Vegas buffet. The cost was reasonable ($25 each I think) and the variety/quality was excellent. For the coeliac, just ask the staff who seat you to be told about the gluten free options and they will get one of the chefs to come and literally give you a guided free tour of the many options on the buffet that are GF. We went twice to Wynn for breakfast and the 1st chef my wife got was better than the 2nd, because the 1st guy even told my wife what items she could have by asking a chef at that station to get a fresh serving, without a certain topping (i.e. breadcrumbs).
Canyon Ranch grill is in the Palazzo (same level as their health spa) and has numerous excellent GF options marked on their menu for breakfast (and possibly other meals). The price was very reasonable too. You get to this restaurant via the guest elevators in the Palazzo (you don't need to stay at the hotel to visit).
Mon Ami Gabi is an excellent french restaurant that faces onto LV Boulevard at the bottom of the Paris Hotel. They have a GF menu with plenty of options. Great service and atmosphere. A little expensive, but well worth it.
Project Pie in MGM Grand do very good GF pizzas for a bargain price. This place is a bit hard to find - you walk through the MGM Grand towards their check-in desks, then go downstairs towards the Brad Garrett Comedy Club and it's on your right.
Serendipity do over the top American food, most of which is definitely not GF. But the Frozen Hotel Chocolate is GF and is plenty big for two to share. It's in front of Caesars.