Sparkfun OpenScale measures both temperature and weight with operating voltage of 5V.
Sparkfun Load Cell Amplifier breakout board is precise and accurate ,reads data from load cells to measure weight.
Pressure-Sensitive Conductive Sheet (Velostat/Linqstat) is a conductive pressure sensitive material that lowers the resistance when squeezed.
Barometric Pressure Sensor - BMP180 Breakout is able to measure the Barometric pressure
Conductive Rubber Cord Stretch Sensor is used to check the resistance.
Flexiforce Pressure Sensor can detect resistance by applying some force on the sensor.
Force Sensitive Resistor from Sparkfun is 0.5 inches long and detects resistance.
Load Sensor - 50kg from Seeed studio is more or less like the weighing scales.
Flexiforce Pressure Sensor - 1lb is a sensor that checks the resistance according to the force applied.
Flexiforce Pressure Sensor - 100lbs detects the resistance according to the pressure applied.