Google Voice is a service which appears more useful after Apple rejected the Google Voice app for the iPhone. The app puts a phone number that can alert you through multiple places or devices and allows you to access it through the Web, in your e-mail and via app. The app also lets you stream audio messages from the Web, without exhausting any mobile minutes.
Thinking Space is a mind-mapping software that organizes the chaos of your mind to create thoughts and productive ideas. This app is availablefor free in the Android market. It is compatible with files created in the Freemind mind-mapping desktop applications.
Advanced Task Killer
This task killing application saves some of the megabytes of memory of your Android device and increases the processor power. The app comes with a widget that you can tap once to kill all open apps. Advanced Task Killer has a free version and a paid version of $5.
Kindle Kindle gives a book reading experience to the Android users, which includes thousands of books.
Astro File Manager
This application stores all the applications on memory card taking back up from phone memory thus cleaning some memory of the device. You can copy/move/rename files, back up apps and send file attachments.
SkyFire It includes a faster web browsing and video streaming.
Dropbox It's a cloud service, that automatically syncs a folder of files between multiple computers. The app extends Dropbox to Android and interacts with other apps to open the files.
Evernote Evernote is a great note taking app and its similar to the Dropbox in the way it saves data. This is a centralized notebook and note creation system that syncs to the cloud. Android operating system's strong integration with Google products and its availability in a wide range of devices gives it an edge over other operating systems.