IPOD TOUCH
It depends if you have AT&T for cell phone service:
(CON) If you do, then the iPod touch is worthless to you because for 100 dollars more you can get an iPhone with a built in 2 megapixel camera, SMS, a data plan, and a cell phone.
(PRO) If you don't, then the iPod touch is the closest thing to an iPhone, and is a great iPod.
Other PROS
Built in Wi-Fi
iPhone without the phone and service
Thinner
Great for movies
Flash memory
Larger screen
Other CONS
Smaller memory
More expensive
Different interface to learn(if you are used to your nano)
iPod Classic
First of all if you are thinking about buying a brand new iPod Classic, They are no longer produced in 30 GB, now they are 80GB for the same price.
PROS
Huge memory
Good for an iPod
Cheaper
Easy to use
CONS
Thicker/ heavier
Less applications and features
Smaller screen
FINAL:
The iPod touch is the one to get if you don't have AT&T. If you do, just buy an iPhone. The iPod classic is still great if you more than 16GB of songs, but otherwise, go with the first to sentences of this paragraph.