These schools are listed as having 2-level grading intervals for the basic science/pre-clinical years (translation: P/F). If P/F = non-cutthroat, then these are the non-cutthroat schools, at least for the 1st 2 years. [Note: does not include schools with 1 year of P/F like P&S, or schools with no exams like Yale]
For your searching pleasure:
http://services.aamc.org/currdir/section1/grading1.cfm
Albert Einstein College of Medicine of Yeshiva University
Case Western Reserve University School of Medicine
David Geffen School of Medicine at UCLA
Harvard Medical School
Keck School of Medicine of the University of Southern California
Loma Linda University School of Medicine
Mayo Medical School
McGill University Faculty of Medicine
Memorial University of Newfoundland Faculty of Medicine
Mercer University School of Medicine
Morehouse School of Medicine
Mount Sinai School of Medicine of New York University
New York University School of Medicine
Northwestern University, The Feinberg School of Medicine
Southern Illinois University School of Medicine
Stanford University School of Medicine
University of Alabama School of Medicine
University of Calgary Faculty of Medicine
University of California, Davis, School of Medicine
University of California, San Francisco, School of Medicine
University of Chicago Pritzker School of Medicine
University of Connecticut School of Medicine
University of Hawaii John A. Burns School of Medicine
University of Kentucky College of Medicine
University of Manitoba Faculty of Medicine
University of Massachusetts Medical School
University of Michigan Medical School
University of Minnesota Medical School
University of Missouri-Columbia School of Medicine
University of Saskatchewan College of Medicine
University of Utah School of Medicine
University of Virginia School of Medicine
University of Washington School of Medicine
Washington University in St. Louis School of Medicine
Wright State University School of Medicine