iPod Nano 4G:
*Rainbow colors [missing unicorns]
*8gb - $149 and 16gb - $199
*Added accelerometer for side viewing and cover flow
*Screen size - 2 inches, 320x240 pixels
*Battery Life - Audio [24hours] , Video [4hours]

iPod Touch 2G:
*Chrome backing housing
*8gb - $229 , 16gb - $299 and 32gb - $399
*Added small speakers for voice playback/phone usage
*Added physical volume adjustment buttons
*Battery Life - Audio [36hours] , Video [6hours]

iPod Classic 3G:
*No more 80gb or 160gb choice, just 120gb now.
*Besides the one unit storage limit, nothing else is changed.

You can head over to Apple.com for some more specs.

Here are some photos: