The net is a powerful tool for harnessing collective memory. The Sonic Memorial Project is a case in point, bringing together sounds recorded by those affected by events on that day. It's a powerful, and very different kind of listening experience to take a tour through their audio archive; perhaps we are too concerned with linear narrative in radio pieces. The way that different sequences of sounds can occur in the project's browser (in my case a Jazz musician followed by a construction worker talking about finding a body in the rubble) somehow makes the experience more moving.
Other memorials are also appearing in virtual form on the net. In Second Life they will be unveiling a virtual memorial as well as a collection of relevant readings about the attacks.