GetaSlogan is continuously holding slogan writing contests at http://getaslogan.com

The contests are sponsored by clients that need a slogan (usually for their business). There are two kind of contests: qualifying and qualified. Qualifying slogan projects are opened to anyone. Qualified slogan projects are only available to those sloganeers that have been finalists previously in Qualifying slogan projects.
There is no admittance fee to participate. Just register as sloganeer at http://getaslogan.com.

Pending payments are released at the beginning of every month via PayPal.