My favorites (and QuietLion's):
Michael Mina (Bellagio) - best tasting menu (get the 7 course!) and excellent a la carte
Bradley Ogden (Caesar's) - a la carte
Nob Hill (MGM) - tasting menu & a la carte
Craftsteak (MGM) - fantastic steak but the sides (veggies!) are amazing, they also have a daily chef's tasting menu