A great way to think about a niche you may get involved with is to write your thoughts down on paper first. It is sometimes easier to think things through when you see them listed in front of you. You want to do this before you start to research niches.
You can then compile all these topics, which should include what you are passionate about, and several other niche ideas. There is a great tool that Google lets anyone use called the Google keyword search tool. It is a helpful tool