Where should I look for open-access articles?

Open access articles can generally be found from two sources.  First, there are numerous journals which ONLY publish open access articles.  Some examples are Nature Communications, JAMA Network Open and BMJ Open.  However, many conventional journals that typically have required a paid subscription are now publishing open access articles as well.  Examples of journals which have numerous open access articles available are New England Journal of Medicine, JAMA, Lancet and many more.