The MaxSonar-EZ1 Ultrasonic Range Finder is a tiny, easy-to-use ultrasonic ranging system that can be easily interface to any microcontroller.
The Parallax PING sensor is cool, but it's more useful when mounted on a servo so it can scan the environment.
The PING))) Ultrasonic Range Finder is a simple to use ultrasonic ranging system that can be easily interface to any microcontroller.
The Parallax TSL1401 Linescan Imaging Daughterboard provides one-dimensional sight to almost any microcontroller.
If you want a really small, compact sensor to detect obstacles coming at your device, the 2-direction sensor kit is just the thing!
The Bittybot Micro Line sensor is a convenient way to build edge or line sensors, especially for MicroSumos!
BittyBot's Nano line sensor kit is a tight and tidy .95" wide pair of sensors for detecting white/black differences, like a line on a surface. Ideal for line-followers or sumo edge detection!
Looking for tiny proximity sensors? The BittyBot ProxDots are very small, and complete with IR modulated transmitter /receivers!
This tidy little 1 row x 8 element thermopile sensor reads the temperature across a 41 degree sweep. And it can control a servo to automatically pan and create it's own thermal image!