For a range of suggestions across schools of various types and selectivity, these colleges appear in a Princeton Review sampling, “Great Schools for Mathematics Majors” (unscreened):
Agnes Scott
Bowdoin
Bryant
Bryn Mawr
Caltech
Carleton
Holy Cross
College of Idaho
Grinnell
Hamilton
Hampton
Harvard
Harvey Mudd
Haverford
Macalester
MIT
Randolph
Reed
Rice
St. Lawrence
St. Olaf
SUNY-Albany
U.S. Coast Guard Academy
UChicago
URochester
Wabash