Swiftkey is a complete replacement for the Android keyboard. It works by learning the words you type most often over time, and uses these to create a predictive database tailored to your individual writing style. Now the software can also link into your Facebook, Twitter and Gmail accounts to more quickly build up that profile by looking at your past messages.
You can customise how it approaches predictive suggestions by changing between rapid and precise modes depending on whether you tend to rely totally on prediction or are a more careful typist. The software is also clever enough to adapt the sensitivity of the keys on the keyboard to compensate for your sloppy typing and help you tap out the right words more often.
Swiftkey X may still be in beta, but this fiendishly clever software is already worth checking out.