When writing for a general audience online (such as readers of wikipedia articles), consider that many people do not have access to a research library, nor paid subscriptions to academic journal articles. If you can find high quality sources that are not behind a paywall, more readers can follow your citations to read the sources. Open Access publications serve this purpose.
Many of the resources linked to here are behind paywalls, but many are also on the open web. This is true of all types of resources, from statistics, to images, to peer-reviewed journal articles. Often, even an academic article that you find behind a paywall, has a legally posted free (Open Access) version that you can link to, so it's worth doing a quick search to find those versions when making wikipedia citations.
Likewise, consider who has written your sources - who are you giving voice to by citing them? (For instance, check out the Cite Black Women movement.)
Use the links/tabs on this page to find a wide variety of sources for your research
And please contact me for research help! Miriam - firstname.lastname@example.org