google is surely your friend... what i found doing 5 mins googling:-

iphone 4 vs ipod 4

back camera
5-mp vs 0.7-mp

ram
512MB vs 256MB

battery size
5.25w/hr vs 3.44w/hr

video out to tv
no vs yes

touchscreen display
IPS technology vs non-IPS technology

phone/gps/3g/edge
yes vs no

calling Alert
ringtone and vibration vs no vibration for FaceTime

etc...