Random Critical Analysis has a lot of articles about healthcare spending, and this one convinced me that US healthcare spending isn't particularly unusual given our standard of living, and it probably won't be easy to lower it (if we even wanted to):
Several other posts cover various objections and show similar graphs using different data.
I think this was the first time I had encountered this argument. The parts that make it convincing are the frequent attempts to show that a particular measure wasn't cherry picked and how the author breaks down data as much as possible instead of just showing the high level view and assuming it's enough.
Iirc this article on climate change made me update notably in the direction of climate change being serious and something worth paying attention to.
Definitely not the first piece of content on climate change I consumed, but maybe first that had a significantly over-the-top alarmist tone to shake me up?
There really isn't a gender-based wage gap; there's a childcare wage gap.
https://www.vox.com/2018/2/19/17018380/gender-wage-gap-childcare-penalty
The content doesn't need to be hosted on LessWrong.
It does need to have changed your beliefs personally. If it changed other people's beliefs, please put this as a comment instead.
Also, the article should be more than simply updating you away from your priors. For example, I'm not interested in things like "learning about a new cause you weren't aware of" but rather in things like "changing your mind about the importance of a cause".
I'm also interested in knowing whether the article was the first time you had come across this point, or it just argued that point better than the previous ones.
Information in other format than articles also work: audio, video, pictures, graph, data table, etc.
This is related to a project idea of tracking belief updates with the goals 1) tracking which information is the most valuable so that more people consume it, and 2) seeing how beliefs evolve (which might be evidence in itself about which beliefs are true; although, I think most, including myself, wouldn't think this was the strongest form of evidence).