I found the blink1 on kickstarter (http://www.kickstarter.com/projects/thingm/blink1-the-usb-rgb-led) and I think this is useful when I want to alert my college. If i’m busy i’ll flag it to red and green when free.

If you interested, you can follow kickstarter link and find more detail. Also software for using it on linux. That’s mean you can use it with RaspberryPI too.