1rst and 2nd generation are the original style released, 2nd generation had a larger HD
3rd generation had the buttons located under the screen and a touch sensitive scroll wheel
Minis, were super small and came in multiple colors
4th generation (not shown) and U2 editions had a raised click wheel integrating all contols in one big button
5th generation had the same form factor as 4th generation and had a color screen to display photos, also known as the iPod Photo
Video iPod came next with a choice of white or black bodies. These have the ability to play videos on the go.
iPod Shuffle is a small slim form factor that is lightweight great for sporting activities.
iPod Nano is another small form factor iPod that has a color screen and a larger capacity than the Shuffle. Availible in white or black.