Well there are several ways of trying to find out what sells well on eBay.
You may want to look closely on the site for the "hot selling products" for one or you can go through the popular searches: Link hidden: Login to view
Our Market Research Lab can also help you out - Link hidden: Login to view
The results are actually based off of eBay searches. You just need to place in an item in mind and check the trend of the product if it's a good selling item in eBay.
Hope this helps!