If you are build something, it should perhaps be simple (but not simple enough ;) ) and something useful to businesses, preferrably smaller ones.
Something related to internet perhaps or something design oriented.
Re-read the article on web science, and see what body of knowledge from there would help.
Read some business stuff on how to start a business. Contact the guy from paypal who gave the presentation at ISNA few years back.
Something to simplify programming? So its not such a guessing game. You think you know how it will behave and then you realize, something is missing. Is TDD an answer to that? Perhaps.
Look at functional.
