I'll repeat advice I've given here many times.
If your goal is trade publication--physical books sold in stores, possibly paired with ebook editions sold online--then you've got homework. Go to three bookstores that are not part of the same chain. For many of us, this involves regional travel, so any time you're going to a nearby city or town, roll a bookstore visit into your timetable.
In the store, find the section where your book would be shelved for sale if it were already out there. With the aid of a camera, photograph or take video the other books in the section, close enough to read titles and authors on their spines. (Be subtle about the camera--silenced, no flash, not in the way of other book buyers.) Be a good person and buy a book written by your competitor.
Now go home and get online. Find out who published every book you photographed. (You'll learn to recognize many publisher's imprint symbols on the spines pretty fast.) Go to each publisher's website and see if they have a way for authors to submit their books. If they do not, then they deal with agents rather than directly with authors. Use your google skills to identify which agents sold these books for their author-clients. Those agents are your A-list to enable access to the "big" publishers. The publishers who do have a way to submit directly may not promote as much, as they tend to be smaller with less money, but they're still real publishers.
Unless you have a valid reason to seek a small publisher (i.e., they have a niche focus and your book is exactly that), aim high. Small presses may seem less scary, and less likely to reject your work, but they're more likely to sell substantially fewer copies of your book--and more likely to fold if their finances or principal/only employee are not healthy.
And as Unimportant said, you want to do your research on any publisher or agent, ideally before you submit.
Maryn, wishing you both luck and success
