Infra-Red Relative Distance Indicator - Shows how close you are.
Musical Pitch sensor - Use musical notes to control your robot.
Acceleration/Tilt sensor - Make a balancing robot.
Air Pressure sensor - Measure pressure in your air cylinder.
Switch Multiplexer - Connect 3 switches to one RCX input.
Passive Infra-Red sensor - Detects movement of people & animals.
Current sensor - Measure how hard your motor is working.
Three-wire converter - Easy-to-use sensor interface for Mindstorms.
Angle sensor - Measures 0 - 270 degree angle accurately.
IR Flame sensor - find a candle or other InfraRed source.
Force sensor - Measure how hard you are pushing.
UV Flame sensor - Withdrawn
Infra-Red Proximity Detector - Withdrawn
Dual Infra-Red Proximity Detector - Withdrawn
InfraRed Relative Distance Indicator (side viewing) - Special Order