Amazon has entered into an agreement to buy digital audiobook service Audible.com. The deal is valued at $300 million, and allows Amazon to dramatically expand its digital audio offerings. While Amazon already offers millions of MP3 songs for download, Audible is probably the biggest name in digital audiobooks, and has a library of 80,000 titles available for purchase.

What's particularly interesting is that Amazon appears to be engaged in an arms race with Apple over global domination of the digital media sphere. Amazon beat Apple to the punch and Apple have been duking it out to see who can offer the largest DRM-free music library, and both services now let users buy or rent movies and TV shows online.

iTunes users have long been able to download audiobooks from Audible and play them on their computers or iPods. We seriously doubt Amazon will kill Audible's partnership with Apple. There's just too much money on the table for that. But you never know.

[Thanks Cris Pearson!]