It is difficult for somebody else to point you in the right direction when it comes to selecting the Niche. Internet Marketing is a HUGE money making Niche. There are many topics or Niche Ideas that evolve from this Market alone. Relation with List Building, Seo, Affiliate marketing, PPC, CPA Networks, Minisites, Keyword research, Product creation, Flipping websites etc etc etc are some of the many examples you can choose from.
Best Thing to do is, see which topic you can best provide content on, Find good JV partners, strike a deal.