Who needs another blog? How brave are you? Build a real estate website. You've got your auth, CRUD, relationships, image uploading/resizing, geocoding via Google, auto PDF fliers and an iCalendar output of inspection times. It's the sort of thing you can just keep adding to until you've got a fully-fledged real estate CRM. Then sell it and make some bank.
(from http://www.reddit.com/r/PHP/comments/3cnufr/what_is_the_php_equivalent_of_a_todo_app/)