The Devantech SRF08 is the advanced model of Ultrasonic distance rangers available, with excellent width-of-field detection, I2C interface, and light-intensity sensor!
The MaxSonar-EZ0 is a very tight-packaged, high-sensitivity single-element sonar module. Much like the very popular EZ1 module, the EZ0 offers higher sensitivity and slightly different coverage pattern
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.