The QTR-1A reflectance sensor carries a single infrared LED and phototransistor pair in an inexpensive, tiny 0.5" x 0.3" module that can be mounted almost anywhere and is great for edge detection and line following applications. This sensor is sold in packs of two units.
The Arduino WiFi Shield connects your Arduino Uno/Freeduino to the internet wirelessly. Connect it to your wireless network by following a few simple instructions and start controlling your world remotely through the internet.
A hand-held GPS that YOU build, and fulfills a different task - no map display, just a pointer for which way to go! Use the Coobro Geo to help you find geocaches, store and navigate between hot fishing spots, or simply find your car after a hike.