Every domain registrar including Godaddy comes up with coupon codes time to time to provide good amount of discounts tom their customers and thus increase sales or domain registrations.
The real thing is that the coupon codes are valid for a limited time like for example say 7 days after which they expire and become invalid.
For getting the best Godaddy working coupon codes, I would suggest you to visit Google or any other search engine of your choice and type search queries like "Godaddy coupons" or "Godaddy discount coupons". This will give you a lot of search results which will include sites and blogs that will have the best working coupon codes.
You can also follow and like Godaddy Facebook and twitter page as they might introduce or publish the offers and discount coupons there as soon as they are launched.
"Winners don't do different things, they just do things differently"