The SRF01 Ultrasonic Range Finder is the latest product from Devantech. It employs Devantech's 2nd generation AutoTune technology which allows ranging all the way down to zero on a single transducer sonar.
Here's a low-cost ultrasonic ranger with I2C and serial interface, using a single element, and a 55 degree sensing angle.
The Devantech SRF05 is a solid, 2-element ultrasonic ranger featuring great range, and selectable 1 or 2 I/O interface
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-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.
Small electret microphone. Useful in acoustic and audio applications, voice recordings.