Android's Amazon MP3 app has gotten an update, and if it's a good one if you have any promo or gift codes, which you can now enter to save yourself some dough.
You have to enter the code before you attempt to purchase a song or album. Press the menu button, the enter the settings, and you'll see the "Enter a claim code" option. Not the best way of doing things, but there you go. Update your app now, and there's a download link after the break if you need it.