SwiftKey X Keyboard Free

This keyboard is pretty amazing. It looks at your sms, your facebook messages and your emails and uses that to guess what word you are most likely to write next. It updates as you type each letter.

So you never actually have to finish what you're typing, just select the predicted word by hitting the spacebar.

It also generates statistics of how many keystrokes it saves you.

Mine is telling me that it has saved me 34% of my keystrokes.

It has a very long trial period, and you can decide if it is worth paying $4 for.