Thinkingwithportals.com

Thinking With Portals is a community based website focused on creating new maps for Portal and Portal 2. The site has been active since 2007. They offer a massive database of custom made Portal maps. They also promote mapping contests regularly such as their Summer Mapping Initiative and Heavy-duty Super-mapping Super-contest.

Contests

 * Summer Mapping Initiative
 * Heavy-duty Super-mapping Super-contest