Freedom to Marry was extremely fucking effective. I use an expletive because of how shockingly effective it was. They turned their website into a manual for activism: http://www.freedomtomarry.org/
I also think that measured by moving the conversation and effects on politics, things like OWS, BLM, etc have been highly effective. We have lots of discussion about wealth disparity, and tons of police departments training their cops more. Among many other effects.