Here are some sites that you can use to create a rubric for your student projects.
Teachnology Rubric Generator
4 Teachers Project Based Learning Checklists
Here are some rubrics that are already created for you. Get some ideas and then create your own.
Multimedia and Web 2.0 Tools Rubrics:
Multimedia Project Rubric
Some of these links and many more links about rubrics and assessment can be found on Kathy Schrock's Guide for Educators: Assessment and Rubric Information.