Expose the Sites
There is information available about the locations of many of the "secret" detention centers'. The map should be able to expose as much information as possible (addresses, phone numbers, email addresses of officials associated with them) so that people could attempt denial-of-service-style attacks on them.
UN Map of Torture contains a large amount of information about secret detention sites. I suggest using the detention map to not only contain information about those that are there, but about the sites themselves so activists can clog email in-boxes, mailboxes, phone lines, etc. with attention. If this information is widely disseminated, it could gain critical mass to disrupt the operations. If the information is made available to the local population it could enable them to take local actions against the detentions.
What kind of resources are needed to get this idea off the ground and/or support it over time?
To do this successfully, there would need to be an individual or group of individuals dedicated to compiling all of the freely available information on these sites. The UN map could be used as a jumping off point, with reformatting to allow easy connection of contact information and detainee information to the appropriate site.
An effort would have to be made to connect with local groups near the sites, so local action could be taken in instances where that is safe. These groups could also be helpful in filling in the details about the sites. The majority of this work could probably be done by volunteers, though it might be necessary to sign-on professional researchers to gather more information for it to work.
How could this idea also be adapted to work in low-tech situations?
This would be a hard one to adapt in full. However, it would be good to format the information in a way that makes for easy printing, so hard copies could be made and disseminated.