Profit Spy was just released a week ago. It scans for profit margins between Amazon and Ebay, so that you know what to sell and can dropship products from one source to the next.
You can read more about it here and click on the watch image to view the demo overview: http://arbitrageprofitspy.com
It only works for Ebay US and Amazon US.
Check out pricematik, recently made by a local member here... looks VERY promising.