There're many big guys in domain industry that you can rely on, however according to me, there're 3 big guys that I usually use to invest a large number of domain on them. 3 of them are Godaddy and Namecheap and Domain dot com
With Godaddy, I usually get big discounts via email, the most percent discount I've got are 40% off, 30% off and 25% off on new orders. More, they have a very professional and comfortable control panel that can help me much in domain management. Very easy to transfer or renew when I need to do. When my domains get expiring, I've always get notification by them, that's very good.
With Namecheap, they have a very good and friendly support team that can help you almost instantly, I've contact them many times and each time was let me very happy and rate them 5 stars in supporting. Namecheap also give monthly coupons that can help you save 25% off on your hosting, VPS purchasing and 10% off on domain transfer/purchase.
With Domain .com, they also usually offer many good discounts for domain .com, .net, .org...they're commonly flash sales that take place in a short time. Their services are also good with fast and friendly support. If you want to buy, you need hurry to catch their flash sale that end up very fast.
So I would like to recommend 3 domain registrars to you. I hope this helps.
Good luck to you!
