Tricider is a website that allows you to quickly pose a question or prompt for a response. People can add ideas quickly to a board with no need to register. Items can be anonymous or names. Collaborators can then upvote ideas or explore them further by adding pros and cons. More collaborators can upvote pros and cons as they see fit.
People can then add alternate ideas for discussion and upvote ideas as they go. You can quickly develop a rich discussion / ideas board.