There was a kickstarter, blink(1) a little over a year ago that did the same thing - http://stackexchange.com/leagues/1/year/stackoverflow/2013-01-01/759517#759517 (and in a nicer package).
I wanted something similar (visual cues for meeting reminders; my "email" system is on a KVM with other "dev" systems). I ended up getting the Dream Cheeky 815 USB Webmail Notifier (http://www.dreamcheeky.com/webmail-notifier) - the thing is designed for email notifications with webmail, but there's an Apache License 2.0 driver and helper app (http://dreamcheekyusb.codeplex.com/), which worked fine to drive the thing - the little command line app that uses the driver had enough functionality (gradual on, color change, and blink) that I didn't need to write any real code.
A little macro scripting, and it was working fine with Outlook.
A little bigger that the other solutions, so maybe not great for a rack (though it's probably about 1U so it would work fine), but works nice sitting on my desk under my displays . . .