Amazon Appstore for Android offers Magic Piano for Android, Songify for Android, and AutoRap for Androidbundled with a $3 Amazon MP3 Credit for free. (You must "purchase" each app separately and you will receive a $1 credit for each one; the credit will be applied to your account automatically after receiving three emails.) That's the best such credit offer we've seen bundled with free Android apps. We've seen previous $1 credits bundled with select games, but they typically only allowed one credit per account. (Google Play also offers each game for free; however, it doesn't include the MP3 credits.) Deal ends December 29.
Update: The offer has since changed. You can still receive a $1 Amazon MP3 Credit; however, it's now limited to one per account. So if you download all three apps, you'll only receive a $1 credit.