The goal of this post is to contain a long number of sources, sorted by topic, to help users find sources for their answers. It's Community Wiki so that everyone can edit add new sources.
The following are sources that are accepted as valid sources to justify your statements, sorted by category. It is by no means an exhaustive list of the accepted sources.
The following are sources that are not deemed reliable enough to justify a statement but still are amazingly useful sources, sorted by category. It is by no means an exhaustive list.