Android (4.1+): Previously mentioned Fleksy has been in private beta for a while now, but now it's available at Google Play for Android users. Whether you just want to customise the keyboard, or turn it invisible so you can see behind it as you type, Fleksy works well.
Swipe to close
The beauty of Fleksy is that it sports some impressive auto-correction, and the whole goal of using the keyboard is that ultimately you won't have to keep looking at your fingers as you type; you'll get a feel for where you should put your fingers and Fleksy will handle the rest. The same autocorrection is available in Android, and after a short tutorial where you're introduced to the app (it may take a little getting used to for people more familiar with traditional keyboards), you'll find yourself touch-typing in moments.
The other nice thing about Fleksy is that it can be configured to use multiple themes, or even to be completely invisible so you can type through it, saving a little screen real estate. Hit the link below to give it a try.