For rooted devices only!
This app will let you conveniently switch out the emoji in your system. Currently available emoji are Google (stock), Samsung, LG, and iOS.
Thanks to gonsa from XDA for providing the font files: http://forum.xda-developers.com/showthread.php?t=2618523
Busybox is recommended, and the app is untested without it.
1.6.3 (July 1):
Fix for HTC devices
More coming soon!