One of my favorite authors/publishers, Vivian Gilbert Zabel , whom I have the pleasure of working with, has led me to an amazing list of resources I just had to share with all of you (being an agent as well as illustrator/designer).
She excitedly told me about her entering Midnight Hours(featuring my first suspense/thriller cover) in an OWFI (Oklahoma Writers' Federation, Inc.) contest and placing 2nd in the unpublished mystery/suspense category.
They gave her some valuable feedback too but not much as her work is top quality and there didn't seem much to critique.
Cooler still, they have affiliates everywhere, so you are sure to find one right for you.