StackExchange themselves use [ClearBits](http://clearbits.net) ([LegalTorrents](http://legaltorrents.com)) for their data dumps. But I think they charge for uploads. And they require stuff to be under a free* license.

<sub>* 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.</sub>