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I use Evernote on every device I use, both mobile and desktop. It is a great tool for doing research online, capturing information, and text editing. I use it daily for all of those functions, and I write thousands of words a day using the editor.
Evernote keeps everything synced with my account in the cloud, always available no matter what device I use. The Android version works well on tablets with an external keyboard for serious writing.
Free on the Android Market
Evernote works well with Skitch, a simple image editor recently purchased by the company. Skitch gets an honorable mention for using with Evernote.