I live in Las Vegas and recommend National Jewelry Center to everyone that compliments on my jewelry. Over the past few months, I've purchased eight rings, a complete pearl jewelry set plus a tennis bracelet and many different chain necklaces. This is the best store to go in all of Vegas if you're looking for high-end jewelry on a budget.
I must admit that Elizabeth S. is correct by stating that some of the sales representatives are judgmental and unfriendly. I've left the store before if the employees I like are not present. If you're worried about who will help you, ask for Ger. She is the best! She is amazingly kind and patient. I've had her pick and pull many types of pieces in and out of the jewelry case... regardless, she doesn't mind a bit.
SIDENOTE: if you're looking for custom jewelry... Go to Anka Jewelry!