It sometimes seems as though what is needed isn't more tools and products, but rather a way to help you to navigate all of them—to determine which products suit your needs as a seller so that you can dispense with the preliminary research and investigation and begin learning to use the tools that are appropriate to your business model.
The Tool of All Tools
Happily, eBay provides an interactive guide that does just this—asks you a few simple questions about your eBay selling business and practices, then recommends the tool(s) that are most appropriate for you. eBay's Tool Recommendations page draws straight lines between seller problems (and related volume) and the eBay-provided tool(s) that are most likely to be helpful in solving them.
While not a panacea (if you're an active seller at all, you should still consider browsing through the aforementioned pages full of tools and tips), the Tool Recommendations page can save you a lot of time when you just want to know which tool solves which problem, right away.
Do you have a favorite eBay tool? Visit the message boards and recommend it to others!