Light Flow has been a go-to app for users that want to keep their device's notification LED flashing appropriately. It gained a lot of popularity with the Galaxy Nexus given stock Android's lack of settings to control the LED, and now the app has been updated with Nexus 4 -- and GMail 4.2 -- support just a few days before the device's launch. It seems to support just about every popular app you could think of, and even more are unlocked in the paid version.
There's a "lite" version of the app that you can pick up at the Play Store link above, and if you like what the developer is doing consider dropping them $2.49 for the paid version.
[Source: Android Central]