Android 4.4 (Kitkat) comes with the option to use the upcoming Android RunTime System instead of the current Dalvik JVM to give a speed boost of approximately 100%.
This basically transforms Android from running in interpreted code using a Just-in-Time compiler to compiled native code.
This is currently giving around a 100% performance improvement in apps, albeit with a 10% increase in app size, with higher gains expected in the final release.
If you have an Android phone running KitKat (4.4) you can turn it on in Developer Settings -> Select Runtime.
This feature is expected to become standard in the next version of Android (4.5) aka Android 5.0