The best site i know is www.superjeweler.com
They have nearly all kinds of jewellery and even do some custome jobs. Just chat with them since they have open 24/7.
Have bought from them many times and the jewelry is beautiful. Have searched the web a long time and havent found anybody beating their pricing. They have a huge selection of natural gemstones and genuine diamonds with certification. The best thing is they also have free shipping to anywhere in the world! They are based in New York and have a lot of reviews from customers.
If you have any questions feel free to ask me i also have multiple vouchers/code (since i have bought from them many times) which reduces the price even more! If interested i can post them