Before you launch, may be even before you have created your product, you must find out what does the market want. Every product must serve a demand or fulfil a need, no?

A very useful way to find out the burning needs of a market is to ask. And The Ask Database is a great way to do this. Or you can The Survey Monkey. However you need to have an in-house list of prospects whom you can ask.

Otherwise, you can consider running a PPC campaign and ask the visitors what they want. A very quick way to verify that your ideas really do have the market potential.