Burgers:
There is a restaurant called BLT Burger in The Mirage...great "middle-of-the-road" burger place. Pretty good stuff.
Also, Carnegie Deli in the Mirage has awesome and huuuuuuge burgers and sandwiches. Borderline deli/fast food.
Italian:
I have only been to Dal Toro Ristorante which is in the Venetian. It's traditonal Italian cuisine and is considered casual dining. Affordable. I'm assuming there are a a few more places in the Venetian or Caesar's that would have good Italian food.
Sushi:
I saw a place called, Koi in Planet Hollywood when I stayed there although I didn't eat there. I'm pretty sure almost every hotel has sushi place. Just ask the concierge where a good one is. He or she will probably refer you to a restaurant/hotel that is sister to the hotel you're staying in.
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