Oh Vegas, how I love thee
As for buffets, Spice Market in Planet Hollywood, and Wicked Spoon at Cosmopolitan is good. I'd skip out on The Buffet at Wynn, it used to be good, now it's just overrated and super expensive.
Hash House A Go Go, already mentioned, is awesome! There is a location in Imperial Palace if you don't have a car to go off strip. Go hungry or share plates because the portions are massive. Strip Burger located in Fashionshow Mall is good as well if you love burgers. There's an Earl of Sandwich open 24 hours I believe at Planet Hollywood, they have awesome sandwiches!! Grand Lux Cafe at Venetian, also mentioned, is good casual food as well.
For a little higher end, Olives at Bellagio is good. Try their beef carpaccio, it is the best hands down anywhere! Steakwise, Delmonico's at the Venetian has awesome ribeye steak, can't vouch for anything else, or CUT at Palazzo. There's a chinese restaurant at the MGM I believe, that was also pretty good but I can't remember the name.
If you do have a car, of course stop by In-N-Out on the way into the strip...
Only available in the state of California and Las Vegas is an exception. Noms!
As you can see.. I go to Vegas to eat.....