Adwords and Internet marketing

I have started exploring Adwords using wordtracker, inventory overture as tools. The purpose is to work on niche marketing. It is quite difficult to think of words that are similar and that is highly searched. For example, I tried to promote en e-book on Adsense. My target are those who are unemployed or who wants to start their own business. Those words that I could think of have been used by others. It is quite difficult to find words that are searched and no ad are shown. The next step is to try out this tool called AdwordEqualiser. Hope it will help to provide some leads on words that are not used.