If you have any inkling that you might want to buy a Kindle ebook before the end of the month, here’s a free $1 credit. All you have to do is hit “Subscribe” on this page to sign up for Amazon’s daily Kindle Deals newsletter, then hit “Claim this promotion” to have the $1 credit added to your account.
You can, of course, unsubscribe from the newsletter whenever you want. I was actually already signed up for it, but I was still able to get the credit.