If you're going with marketing a website (as suggested by many in this thread) but can't decide on a niche, you could elect to go completely in the other direction, and create a general interest/catch-all news trends type blog, with 6-7 basic topic categories. From there, now you can take any viral or Google Trends type phenomenon and test how to explore it, for Adsense, affiliate, e-book promotion or other way to bank.
Look at other for-real sites that adopt this format for insights as to how to build real traffic to it, or best monetize it. "What works, what doesn't, what does it turn out you're better at?" and so on. Your own catch-all site might end up acting as a "home room" to build other, truly niche digital marketing projects.