One thing that can be sold on the web is access to information! This usually comes in the form of subscriptions to newsletters, or sales of books or reports. Check out these report titles for example. One advantage of selling information, or access to the information, is that these can be delivered electronically. This means there is no product to manufacture or ship. All you need to do is set up a mechanism for delivering the content, such as a web site, and everything (except marketing) takes care of itself.
People crave information that appeals to their basic needs and will somehow educate or enlighten them. Simply by putting your own specialized information into e-books, manuals, reports, e-zines or newsletters, you can start putting a hefty price on information you have no doubt been giving away. Makes sense doesn't it?