Sign up for John Matthew Fox's emails (https://thejohnfox.com) for great resources, such as this list publishers who may be looking for the type of book you're writing. You can submit to them directly without having to go through an agent.
30 Small and Indie Publishers. A great list of small, independent publishers of fiction, nonfiction and poetry.
30 YA Publishers. Most of these publishers accept non-agented submissions (which means you can start submitting today).
44 Publishers Looking for Short Story Collections. Everyone says publishers hate short story collections, but this list disproves the rumor.
30 Children's Book Publishers. All these children's books publishers accept submissions directly from authors.
40 Romance Publishers. If you've got lovestruck characters or a novel with sensual scenes, read this.
The Best Christian Publishers. Writers of faith, these publishers appreciate religion in fiction and nonfiction.
33 Publishers for Novellas. Have a piece of fiction too long for a short story and too short for a novel? Check this list out.
20 Independent Publishers who won Literary Awards. These are mostly scrappy publishers who manage to put out quality books that win awards.
Erica Verrillo's blog "Publishing ... and Other Forms of Insanity" offers a list of publishers accepting unagented manuscripts. You can also subscribe to her postings. https://publishedtodeath.blogspot.com/p/publishers-looking-for-authors.html