Learn more about online sourcing at www.fbamaster.com
A very good site that can be used to find items that can be resold online for more (through Amazon or eBay) is www.keepa.com. This site tracks the prices of items sold on Amazon and shows it in a graphical format.
This video shows you how I use Keepa to find products to source online. I give some example of previous products purchased and also give some insight into other items that might be of interest.