WeCollaborate.com is built on the Ning.com platform, and one of the apps that can be added is for the Box.net service. Box.net has a free/personal plan that allows up to 5GB of storage. So, I added this feature and am interested in seeing how it works for you.
Hover your mouse over "Members" and click on "Repositories." I think Box.net will allow you to sign up, and then be able to create folders and save files there. What I don't know is if you can make a folder "public" so others can access it--I'm not sure if Box.net handles that, or if there would be any way to display that folder here.
Experiment and let me know!