It's that time again, music fans. It's time for Amazon to open its vaults and transform itself into the digital equivalent of the bargain bin in your favorite used record stores. Through the end of October, the massive online retailer will be selling one hundred mp3 albums for just $5 each. It's a great time to stock up on the staples and fill in those massive gaps in your music library. We've all got 'em, no matter how rampant our musical fandom, but we can always get that much closer to owning the complete back catalogs of good music. Here's the best Amazon has to offer this month.