Android L "Material" keyboard rocks
Not sure how to describe it...it is FAST...like response times are really really quick. Animations feel a lot more fluid. I used to think Swiftkey was fast, but this feels like another level.
I didn't expect to like it. Swiftkey looks better in screenshots. But the L keyboard is just awesome. I am already typing much quicker on it. The keys are easier to see, the spacebar is easier to see, and all the emoticons are still there. Voice input seems a lot quicker as well.
[APP][4.0+] Android L (5.0) - Apps, Keyboard APK, Wallpapers, Fonts, System Dump, etc - xda-developers
I had to be rooted to use it. If you are using a non-nexus device, you might not need to be rooted. You install a 3rd party keyboard (any...I already had Swiftkey installed), and then delete or move the "LatinImeGoogle.apk" from your system/app directory. Reboot. You can now install the new keyboard APK:
[APP][4.0+] Android L (5.0) - Apps, Keyboard APK, Wallpapers, Fonts, System Dump, etc - Post #92 - XDA
If you are using a non-Nexus device, you may not have to move anything. You might just be able to install the APK like any other.
This will work on KitKat for sure, and at least one guy is claiming to have it running on JB (4.2.2).
(remember that you can always install the current keyboard again if you want...it is called "google keyboard" in the Play store).