ASTRO FILE MANAGER
One of the odd things about transitioning to a smartphone from a traditional PC is the lack of visibility into the underlying file system. Sure, you can go through a sub-menu under "Settings" and look at what's stored on your Android device that way, but a dedicated file browser is a must for many. Astro has been the most popular option for some time.
Access to your Amazon digital content from your Android device? Yes, please. The official Kindle app is a must-have particularly for tablet users, and even though Google's doing its best to supplant Amazon in e-reading with its Google Play Books feature, Kindle is still the one to beat.
Most kinds of information can be captured and organized with Evernote, a note-taking app that you can use on Android, iOS, Windows Phone 7, PC, Mac and in browsers. The usefulness of Evernote is tough to overemphasize for knowledge workers in a number of fields -- journalism included.