CES was originally a research-based organization, but recently shifted to advocating Approval Voting and trying to get it implemented. (I think they should rename as the Center for Approval Voting.)

Their forum and Google Group for discussion of voting systems were good resources, but are now being shut down

https://forum.electionscience.org/t/archiving-the-forum-july...

https://groups.google.com/g/electionscience

"This change reflects CES’s gradual evolution from an academic organization to an advocacy organization."

A volunteer-run forum has been created to replace it, but is pretty quiet so far.

https://www.votingtheory.org/

http://reddit.com/r/EndFPTP is also a good "non-partisan" resource, as well as https://electowiki.org/wiki/Main_Page