If you're already onto ebay or are planning to be, you might want to check out this review of the AuctionInspector software.

From the review:

"The inspectors went through and found posts for my potential buying market. They also checked to see if sellers are high in this area. Then Auction Inspector put the demand in a rank order and compared it with seller's response. I had my list of possible items and knew who was running to take advantage of what. Next thing I knew I was listing high demand items and I was making money with my store."