The GP2Y0A21 Sharp distance sensor is a great way to add obstacle avoidance or motion sensing to your robot or any other project. With a detection range of 4" to 32" and an analog voltage indicating the distance, this sensor is very easy to use.
The InvenSense MPU-6050 sensor contains an accelerometer and a gyroscope in a single chip. It is very accurate, this sensor is used in self balancing robots, drones, smartphones, etc. The sensor uses the I2C-bus to interface with microcontroller.