Check MacMall.com.
Others are TigerDirect.com, NewEgg.com, JR.com, and even Amazon.com.
I have personally used each of these more than once. Great all the way around. Service is tops at each.
You can get the 1st Generation 16gb for 399.99 or less. If you find a list price higher than that, move on (remember, that is for the 1st Generation).