You need to go the Flamingo Buffet. Really really good food. They've got the best lunch options such as all kinds of soups and stews, fresh pizzas, fresh salads, great fresh seafood, all kinds of roasted meats etc.
If you want hardcore variety when it comes to sweets and desserts, you need to visit Harrah's Buffet. Best best best freshest sweets.
This place also has a really amazing selection of shrimp and seafood, such as crab legs and broiled fish.
For breakfast, go to Treasure Island Buffet. They have the best variety of omelets, rolls and croissants, breakfast treats such as danishes. This buffet also offers the best sushi in Vegas. Really really good seafood as well.
I went to Vegas twice. Once for my honeymoon spending 5k in 10 days. We didn't know the place that well so we ate at restaurants. We didn;t know about the buffets until we went back and when we went back the second time, we spend about 1k in one week, this including drinks and other things.
Vegas buffets are probably the best and very spacious. Many people go there therefore there is a huge turn over in food. This is good because it ensures the freshness and its not just sitting there for hours. Also consider going to Denny's. Great restaurant with an awesome menu selections. Really reasonably cheap compared to 80 bucks you'd expect to spend at a very mediocre restaurant down there (yes that happened to us when we went to Treasure Island for a dinner....it was horrible and very expensive)
stick to the buffets i listed above and you'll be very pleased!
Have fun!