The sensors in all iPhones released as of May 2016 are:
iPhone 2G:
- Proximity sensor
- Ambient light sensor
- 2MP Camera
- Accelerometer
iPhone 3G:
- Proximity sensor
- 2MP Camera
- Accelerometer
iPhone 3GS:
- Proximity sensor
- Ambient light sensor
- 3.15MP Camera
- Accelerometer
- Compass
iPhone 4:
- Proximity sensor
- Ambient light sensor
- 5MP Camera
- Accelerometer
- Gyroscope
- Compass
iPhone 4S:
- Proximity sensor
- Ambient light sensor
- 8MP Camera
- Accelerometer
- Gyroscope
- Compass
iPhone 5:
- Proximity sensor
- Ambient light sensor
- 8MP Camera
- Accelerometer
- Gyroscope
- Compass
iPhone 5C:
- Proximity sensor
- Ambient light sensor
- 8MP Camera
- Accelerometer
- Gyroscope
- Compass
iPhone 5S:
- Proximity sensor
- Ambient light sensor
- 8MP Camera
- Accelerometer
- Gyroscope
- Compass
- Touch ID fingerprint scanner
iPhone 6:
- Proximity sensor
- Ambient light sensor
- 8MP Camera
- Accelerometer
- Gyroscope
- Compass
- Barometer
- NFC for Apple Pay
- Touch ID fingerprint scanner
iPhone 6 Plus:
- Proximity sensor
- Ambient light sensor
- 8MP Camera with OIS
- Accelerometer
- Gyroscope
- Compass
- Barometer
- NFC for Apple Pay
- Touch ID fingerprint scanner
iPhone 6S:
- Proximity sensor
- Ambient light sensor
- 12MP Camera
- Accelerometer
- Gyroscope
- Compass
- Barometer
- NFC for Apple Pay
- Touch ID fingerprint scanner
- Pressure sensitive display
iPhone 6S Plus:
- Proximity sensor
- Ambient light sensor
- 12MP Camera with OIS
- Accelerometer
- Gyroscope
- Compass
- Barometer
- NFC for Apple Pay
- Touch ID fingerprint scanner
- Pressure sensitive display
iPhone SE:
- Proximity sensor
- Ambient light sensor
- 12MP Camera
- Accelerometer
- Gyroscope
- Compass
- NFC for Apple Pay
- Touch ID fingerprint scanner
iPad 1:
- Accelerometer
- Ambient light sensor
iPad 2:
- 0.7MP Camera
- Accelerometer
- Gyroscope
- Compass
- Ambient light sensor
iPad 3:
- 5MP Camera
- Ambient light sensor
- Accelerometer
- Gyroscope
- Compass
iPad 4:
- 5MP Camera
- Ambient light sensor
- Accelerometer
- Gyroscope
- Compass
iPad Air:
- 5MP Camera
- Ambient light sensor
- Accelerometer
- Gyroscope
- Compass
iPad Air 2:
- 8MP Camera
- Ambient light sensor
- Accelerometer
- Gyroscope
- Compass
- Barometer
- Touch ID fingerprint scanner
iPad Pro (12.9"):
- 8MP Camera
- Ambient light sensor
- Accelerometer
- Gyroscope
- Compass
- Barometer
- Touch ID fingerprint scanner
iPad Pro (9.7"):
- 12MP Camera
- Ambient light sensor
- Accelerometer
- Gyroscope
- Compass
- Barometer
- Touch ID fingerprint scanner
- Sensor for True-tone display
iPad Mini 1:
- 5MP Camera
- Accelerometer
- Ambient light sensor
- Gyroscope
- Compass
iPad Mini 2:
- 5MP Camera
- Accelerometer
- Ambient light sensor
- Gyroscope
- Compass
iPad Mini 3:
- 5MP Camera
- Accelerometer
- Ambient light sensor
- Gyroscope
- Compass
- Touch ID fingerprint scanner
iPad Mini 4:
- 8MP Camera
- Ambient light sensor
- Accelerometer
- Gyroscope
- Compass
- Barometer
- Touch ID fingerprint scanner
iPod Touch 1:
- Accelerometer
- Ambient light sensor
iPod Touch 2:
- Accelerometer
- Ambient light sensor
iPod Touch 3:
- Accelerometer
- Ambient light sensor
iPod Touch 4:
- Accelerometer
- Ambient light sensor
- Gyroscope
- 0.7MP camera
iPod Touch 5:
- Accelerometer
- Ambient light sensor
- Gyroscope
- 5MP camera
iPod Touch 6:
- Accelerometer
- Ambient light sensor
- Gyroscope
- 8MP camera
Edit 1: Added all iPads and iPod Touches to the list.
I left out the front facing camera somehow! I'll add that as soon as I can.