Here are some sites that you can use to create a rubric for your student projects.
Rubistar
Teachnology Rubric Generator
4 Teachers Project Based Learning Checklists
Rubric Machine
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:
Animoto Rubric
Blogging Rubric
Multimedia Project Rubric
Glogster 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.