In addition to the information vincente mentioned, I recommend:
Subjective quality of undergraduate education ( e.g. 5 = best, 1 = worst)
Satisfaction with program (same type of scale)
general GRE scores
Also, it might be useful to have a system where you can display information by school, for instance
GPA scores for for people who were accepted at school X, or GRE scores for school X, etc
And it might be fun to see some additional plots, like GPA vs. GRE score, # schools applied to vs. # schools accepted at, scores vs. gender, quality of education vs. GRE, etc.
I would use the plots at http://www.studentsreview.com
as a guide.
This is a unique opportunity to get a lot of information for the member base of this forum. Plus I think it would be cool to see where correlations are. This would allow to REALLY see where the biases are.