This is a very cool application that I think you will like ... no, I know you will like it.  A lot of people want the ability to know when they get an email from a specific person and to have a custom notification when it arrives.  Well, now you can have your cake and eat it too because there is a solution from Watchflag!

Watchflag runs on mobile devices to scan incoming messages and alert you based on rules you define. It's like ringtones for your email.

Watchflag is software developed for mobile devices to provide you with custom alerts when new messages arrive. It will screen each email or text message and compare it with a set of rules you define. You can make rules based on the sender, subject and importance level of the message. When a message is received that matches a rule, your phone will light up, play a sound, vibrate, flash the camera's LED, display an "acknowledge screen"... or do all of the above!

via Jason Langridge's WebLog