There are many places in the web where people are collaborating, for example in YouTube, someone will post a video, and the people will comment on it, saying where is that place, what song is playing in the background, if there is some good comment people will vote it up and also the can post reply videos to it.
In the Encyclopedia of Life, people collaborate to catalog species, the post photos, and videos and all kinds of scientific info about it. So if there is a new paper publish on it, it could be linked to it.
In most new websites, people can comment and debate and complete the news. There are sites like WikiNews and AllVoices where the visitors are the ones who create, edit and upload the whole story, the can post links to other sites with more content, to blogs, upload more images, insert a map with the location of the news, videos, etc.
We also have sites like Pachube.com, that enable people to store, share & discover real-time sensor, energy and environment data from objects, devices & buildings around the world. The you can do all kind of creative things with that info, like this:
But with all this we are still missing a big part of the equation. A website where people can post there needs or ideas, like for example, maybe someone has come to realize that the way we do laundry at home is still quite tedious and so last century, so we might post the need for a new laundry system.
Then people can come in an collaborate to help design the new system and patent it and maybe even sell it to some companies. So maybe someone will help with the part of the system that helps with identifying the stains and someone else pitches in with some idea about how to inject the stain remover in that area of the clothes, and so forth and so on.
We need the get something like that going, it is not possible that with so many collaborative tools on the net we are missing the most important.