I would like to suggest a beam sensor for a useful product. Being able to detect vehicles crossing, etc with an outdoor rating would be greatly helpful.
[Beam Sensors][1]
I’d also like to point out that if people find a device that they would like to try their hand at integrating, send us a note (build@smartthings.com) letting us know what and how it will be awesome and, in many cases we’ll buy the device and send it your way.
My project actually used an ultrasonic sensor, not a beam or curtain sensor. But is does show that with the ST Arduino Shield, yu can make almost any project into a SmartThings one. A little code and a few wires and wa-la