You want them for you iPod so will be in use on the go?

If so you don't really want full cans and would be better of with canalphones.

From your brief requirements I would get Head-Direct RE0:
http://headphones.com.au/psingle?productID=413

I have them and they are fantastic value for money, used to cost around $300. Light on the bass but brilliant at everything else, matches your description.

But if you are after full cans then look at:
http://headphones.com.au/psingle?productID=19
or
http://headphones.com.au/psingle?productID=180

None of these need an amp.

Forget Sennheiser.