I am currently building my third product. The idea "seed" for the third product came about when I was at a SaaS conference and met a developer influencer-person. He also runs a Ruby on Rails recruitment agency and was asking me if my current product could solve a problem he has been having.
I kinda filed that conversation in the back of my mind. A month later I met a father of one of my children's friends. He happened to run a recruitment agency and that idea popped up in my head so I asked him what he thought of that issue. He told me he has had the issue and knew of a handful of other agencies having the issue.
I asked if he would pay for the solution and threw out "$200/month" as an idea and he said it was a nobrainer.
Enter, my new product.
TLDR? Talk to people and learn what issues they have and find one they are willing to pay to make go away.