I had a customer recently ask me for a way of having the LED only flash on a device when new email came in (the customer was migrating from Blackberry which does this)

Well I spotted this solution called LED Alerts over on Smartphone Thoughts which provides the ability to set custom notifications using the LED in the device.

For devices such as the Samsung Blackjack 2 you can even use different colours for different alerts!

The solution LED Alerts also provides:

Activate external LED based on specific event
Control 7 different LED colors on BlackJack II*
Ability to assign different LED to each event*
Activate LED for missed calls
Activate LED for new Voice Mail
Activate LED for New EMail Message
Activate LED for New SMS Message
Activate LED for New MMS Message
Activate LED for Missed Reminders
Manages Simultaneous Active LEDs
User Selectable Active LED Duration

You can download a free 7 day trial HERE