The reason we are interested in DMOZ, eBay and Amazon and your local shopping mall is that they have lots of categories to dig into. Let's take a look:
DMOZ Major Categories: Are you interested in any of these?
We click on KIds and Teens:
Now we Click on Games
Now, you can at DMOZ click on Computer and Video or what ever you want. Keep digging until you find a niche that you want to study and work. You can look at forums in this niche, get to know what the needs and wants of the market are, what problem in the market that you can solve.
Repeat this Process for eBay and Amazon and by walking in the mall. Just remember that things you can buy in the local store, like commodities, bread and chewing gum and monkey wrenches and such, are not good niche markets. They are not niche markets.
Next: Finding More Areas of Interest at UberSuggest.org