Rift's Mobile Authenticator for Android devices has arrived! It's available as a free download in the Android Marketplace. A version for Apple devices in the works, and Trion Worlds hopes to release additional versions for other platforms and devices in the future.
Link to news story: http://rift.zam.com/story.html?story=25808
I downloaded the authenticator for my Motorola Droid and it works without any issues.