I think you're playing yourself down here. You can build websites, so you have the perfect skill set to solve (almost) any problems.

Just get out there and find out what problems people have. Ask a bunch of people which websites/apps drive them crazy.

With a bit of luck they will mention ones that they use regularly or pay money for. Once you find a niche product idea, come up with a way you can test your hypothesis, Lean Startup style.