Stack Exchange themselves use ClearBits (LegalTorrents) for their data dumps. But I think they charge for uploads. And they require stuff to be under a free* license.
* Free in the Free Software sense, or one of the non-Free Creative Commons licenses, such as ND or NC. I'm not sure exactly what their requirements are, but it has to allow unpaid redistribution, anyway.
The above is no longer true. ClearBits have closed down, and the SE data dumps are now hosted on Archive.org.
