Facing History is a fantastic organization that has informative seminars and well developed resources on issues of human rights, genocide and justice. If you have not physically or virtually attended one of their workshops I highly recommend you do! Until then check out their website for their units, lessons, resources, and online modules.
Reading Like a Historian: Stanford History Education Group
I have become a big fan of the pedagogical model of Reading like a Historian. I think their methodology and approach provide a great frame for inquiry work. They also have complete lesson plans that you can use. I have never used one in full, but have borrowed some of their excerpts of primary and secondary sources to bolster my own curriculum.
The Choices Program at Brown University
The Choices Program is not free. If your school is willing to pay or if your school has already purchased a set of curriculum from choices you are lucky. I am not the biggest fan of their secondary resources because it reads like a textbook and my students do not absorb as much from simply that type of learning. What I do like is their course ideas. The course I created called "On Violence" was largely inspired by their curriculum on India and Pakistan. The other great thing about the Choices website is that they have these short videos of interviews with professors about a range of social studies topics that I have found to be great resources for the students writing in depth research papers.