Just sold my 3GS 16GB on eBay for £380 (around $550), was quite surprised what people will pay for a used phone when you can buy a brand new PAYG one for £449.
how much did u pocket in the end after postage, ebay and paypal fees?
i got £350 for mine out of ebay which i thought was 'ok' considering it was a fresh replacement from the Apple Store and had 3 months warranty on it.