This is by no means a comprehensive list (and neither is my first post on the subject), but it might prove useful anyway. In case you...have a sudden need to read spanking fic. Or you're writng a research paper or something. I don't know.
Vicki Blue's Spanking and Domestic Discipline is a site dedicated to real spanking in adult heterosexual relationships. Well, you can't say it clearer than that. The site has essays, fiction, recommended reading, and you can sign up for an OTK (over the knee) newsletter. There are links to "sister sites," too, such as RetroSpank and Bethany's Woodshed. Those seem to be part spanking, part time travel; there's a tinge of nostalgia to a lot of spanking sites, actually. (See? You SO COULD write a paper about this.)
Elizabeth Burns' Domestic Discipline offers sound effects: In this site I have a number of things available to give more information about different types of DD relationships, as well as the ability to hear actual scoldings, spanking stories, letters and thoughts about DD relationships and details of actual DD relationships. I offer things in both written and audio clip format.
There is a Yahoo group for Domestic Discipline Personals, apparently still active.
There are books of DD stories; I'm just linking to one, because the "customers who bought this also bought" feature immediately produces a bunch more.
And Seek Discipline covers a broad range of things, including domestic discipline.
Animal Characters and a Sale! - A lot of my favorite romance authors include animals in their romances. In Regencies, we often have horses, but other animals, usually pets, can add fun to...