The Network for Public Education is an organization started by Diane Ravitch and Anthony Cody that seeks to undermine anything that would undermine public education (this site is agenda driven). You can find their many reports about charter schools on their site.
Standing in opposition to the Network for Public Education is the agenda driven National Alliance for Public Charter Schools. This site has its own set of information about charter schools (limited but helpful) that comes from an assumption that choice is critical.
The Brookings Institution has information about charter schools. Some titles include, “Charter schools? Good or bad for students in district schools?” and “What are charter schools and do they deliver?”
The Center on Reinventing Public Education provides some research and opinion pieces by people who think about charter schools. Search “charter school’ and then look at the “Filter by related publications’ list on the right. You’re likely to find resources that can be helpful.