You are about to enter the world of shareware. You could setup a web site and advertise it (not here of course ;-). You can search for the word shareware and list your application at any sites you can find that post shareware. You would have to add the functionality to disable the application if the user does not register and purchase a license or key from you. I have never done any of that but I have been around the web to know what it looks like. It will be hard to sell your application without give the users a trial version so that they can test drive it. My humble opinion of course.