All of the other $0.99 codes have expired but I just found out about a new one which lets you register or transfer up to 3 dot coms at $0.99 each. It’s only available to customers from the US or Canada, so I can’t test it myself.
If you’re not from the US or Canada, you’ll receive an error message after making the payment.
Here’s the code:
Edited: if it doesn’t work, try the code 98CENTS
Both codes are only valid for customers from the US and Canada.