National Data Sources
Phds.org (lots of ranking, links)
National Center for Education Statistics (New report)
AAUDE Data and Resources (good starting point for any data needs)
AAUDE Reports (see especially Glossary of Graduate Education Terms and AAU Graduate Education Taskforce: Progress, Plans, Issues)
The Center for Measuring University Performance (just moved to ASU)
Humanities Indicators (JUST RELEASED!)
For information about the relationship between GRE scores and performance, see “A Comprehensive Meta-Analysis of the Predictive Validity of the Graduate Record Examinations: Implications for Graduate Student Selection and Performance,” Psychological Bulletin, 2001, vol. 127, no. 1, 162-181, N. Kuncel, S. Hazlett, and D. Ones, authors.