DidYouKnow is a repository of all sorts of uncommonly known and verifiable factoids.
1. Verifiable, online, free : No paywalls or references to offline only materials.
2 . Sources, not discussion: Wikipedia is not a valid source for this reason. However, it is an excellent repository of sources. Simply find the citation for any given fact in an article, verify, and link that instead.
3. Causation, not correlation: People who spend at least 48.3 minutes a day jumping on one leg while quoting Monty Python in reverse are less likely to have children who suffer from polyorchidism? Awesome! Not appropriate.
4. Multiple sources? Sure! When using multiple sources include them at the top of your post with a brief description of pertinence to allow others to check them out easily and quickly.