No promo code needed. All you nee to do is search in Google for “GoDaddy” and click a link on their AdWords ad “$0.99 Domain Name Sale.” It looks like GoDaddy is having this promotion all year long. If you have problem finding it, try to search for “GoDaddy” in an another browser or clean a history and cookies of your currently opened browser – AdWords ads use frequency capping.
The method described in this post unfortunately works only once for one account.
For those who need more saving, here is a GoDaddy promo code
“cjcFW199” – which will let you buy .com domain for just $2.17 (it works as of September 16, 2013)