Here is a Quickie comparing iPod Nano with iPod Mini:
The iPod Nano is very tiny. In fact, it’s about the size of a portable flash drive (those little memory sticks that people walk around with and plug into their laptops).
The iPod Nano has all of the features of the iPod mini, with the real differences being size, storage capacity, and technical scalability.
Similar to the mini, the nano also has a color screen, and the beloved grey wheel that must be depressed in order to work (which is a feature that Apple added based on feedback from early iPod consumers).
The iPod Nano weighs – get this – an ounce, which MacWorld equates to the heaviness of 6 credit cards. Here is a must read free ebook at Want to Learn.