Online Rubrics 

The Buck Institute has a ton of downloadable and customizable rubrics, including a rubric for rubrics!  These stress the 4 Cs which should be included in any good PBL rubric

From British Columbia organization LearningNetwork.org

• Project Based Teaching Rubric
• Project Design Rubric

Rubrics for Core Competencies

• Critical Thinking Rubric
• Creativity and Innovation Rubric
• Collaboration Rubric

For Projects and Presentations

• Gr. 9-12 Presentation Rubric
• Gr. 6-8 Presentation Rubric
• Self-Reflection
• Project Assessment Map
• Project Assessment Map Sample

This is a free, fairly general TPT download.  Other PBL resources you can pay for.

This may be helpful for evaluating the final products themselves

Here are some guidelines for developing rubrics