Where and how can I save my notes online and categorize them too ?

I generally like to make notes over some topics that interests me. When I find something related to these topics somehow, either from reading magazines or articles or hearing from someone else I want to add it to these notes of mine. So I want to save them somewhere online so that I can edit them whenever I want to from anywhere with ease. And yes I want to keep them to myself and not public. Any such sites?