Nature's Best Photography Magazine

* Has photography contest including picture of the week

National Audubon Magazine

* Has photography contests

Naturescapes.net Online Magazine

* Does not have photography contests, however one can upload images for critique

BirdWatching

* Has a weekly photography contest

National Wildlife Magazine

* Has photography contests

Nature Photographers Online Magazine

* One can submit photos to the Weekly Challenge critique gallery

Landscape Photography Magazine

* People can submit photos for a multitude of purposes

Outdoor Photographer

* Has photography contests

DiscoverWildlife.com

* Has a monthly photography contest

pdn (Photo District News)

* Offers a myriad of photography contests including sports

I-Shot-It
* Offers a plethora of contests for one to enter.  However, I have yet assertained whether or not this site is cheesy or not.