Not that many appearance changes occurred over the years but there subtle differences as Apple software itself became further improved. In the latest updates for this product multiple colors have been offered bringing a somewhat new outer appearance to the iPod Touch.
1st generation
Release Date: September 5, 2007
Storage: 8GB, 16GB, 32GB
Battery: 22 hours of audio and 5 hours of video battery
Features: Wi-Fi and a multi-touch interface, internet browser and app store
2nd generation
3rd generation
4th generation
5th generation
6th generation
Release Date: September 9, 2008
Storage: 8GB, 16GB, 32GB
Battery: 36 hours of audio and 6 hours of video battery
Features: volume buttons, speaker added, app store now standard
Release Date: September 9, 2009
Storage: 32GB, 64GB
Battery: 30 hours of audio and 6 hours of video battery
Features: voice control and bundled remote earphones
Release Date: September 1, 2010
Storage: 8GB, 16GB, 32GB, 64GB
Battery: 40 hours of audio and 7 hours of video battery
Features: thinner design, HD video recording, two cameras, white colored version was later released
Release Date: September 12, 2012
Storage: 16GB, 32GB, 64GB
Battery: 40 hours of audio and 8 hours of video battery
Features: Siri, new aluminum design, colored case options
Release Date: July 15, 2015
Storage: 16GB, 32GB, 64GB, 128GB
Battery: 40 hours of audio and 8 hours of video battery
Features: five colors, 128GB new model and better internal features