Is there any difference in size between 3G 10/15GB vs. 20GB iPods and 30GB vs. 40GB iPods?

The 10/15GB iPods are the same dimensions as the 20GB iPod.

The 30GB iPod is the same dimensions as the 40GB iPod.

All of these iPods (10/15/20/30/40GB) are known as 3rd generation (Gen 3, 3G, docking) iPods that use a dock connector for charging and syncing.