Amazon has launched a public beta of Amazon MP3, its new digital music download store offering DRM-free 256kbps MP3 files. According to Amazon, the service boasts “Earth’s biggest selection of a la carte DRM-free MP3 music downloads.” The service currently offers over two million songs from more than 180,000 artists. Individual tracks are available for $.89 or $.99, with full albums available from $5.99 to $9.99. In addition, the…