After just going thru science fair with my daughter, how about:
MOST WORK DONE BY PARENTS?
or
Most work done by the student
I guess the latter would be more diplomatic. I mean really. Should a second-grader really be concerned with the DNA of a strawberry?
You could do prizes such as "most colorful, most creative, involved more people than any other...

"
Parents, please. Take one of the MANY MANY questions your child has asked over the past few weeks and USE IT as a jump-off point to help them learn. My DD's project was one she had a natural question about and was SO simple...yet turned out really well. The question?! "Can you touch a rainbow?" with a follow-up of "What would it feel like?"
Kids are naturally curious and have such great questions that would never require them to steal an idea off the internet. The point of a project at this age is to teach them the scientific method, not to impress people with knowledge they don't really need at age 8 or 9!
Ok, this is me, jumping off the soapbox. I think having the class give awards is a really great thing. You could just take the awards and fill them out with their name...and then write in what is a winner about the project after you see it!