If a speaker, vibration motor, and an on-device notification light aren't enough to grab your attention when a new message comes to your phone, you need a more extreme option. The developer of HueNotifier Beta has provided one: an impressive sync between any Android 4.0+ device and Philips' range of Hue connected LED lightbulbs. After installing the app and setting it up, new notifications from any app can be assigned to pulsate the light bulb or bulbs in any available color.
The app is pretty basic at the moment, but seems to have all of its bases covered, with easy setup and quick modifications. Pulses can be set to any length of time, though it appears that a notification can only flash once. Users will have to set up an Accessibility service to enable it (Settings>Accessibility>HueNotifier). There is one potentially deal-breaking bug in the app right now: the accessibility setting tends to reset after you power your phone or tablet off. Here's a short demonstration of the app in action - apologies for the poor quality, but it appears to be the only one available.
You'll need the Philips Hue base station and at least on Hue lightbulb to get started. After spending that kind of dough on some fancy lights, another $1.29 for the HueNotifier Beta app shouldn't be an issue. Don't forget the official Hue management app as well.