Printful – (Free) This company automatically fulfills all orders for you and ships them from their warehouses. It’s what we use on our website for all of our products. Printful takes a small cut of everything you sell, so there is no upfront cost to you. Click here to check it out.
If you know of resources that I did not include above, please add them to the discussion (affiliate links are fine as long as you have used the service). And if you are looking for specific suppliers or have a questions, feel free to ask.
I will be constantly updating this list until we have a monster directory, so check back often.