One philosophical school which has historically had a close relationship with process philosophy is American pragmatism. Whitehead himself thought highly of William James and John Dewey, and acknowledged his indebtedness to them in the preface to Process and Reality. Charles Hartshorne (along with Paul Weiss) edited the collected papers of Charles Sanders Peirce, one of the founders of pragmatism. Noted neopragmatist Richard Rorty was in turn a student of Hartshorne. Today, Nicholas Rescher is one example of a philosopher who advocates both process philosophy and pragmatism.
What pragmatists did Whitehead acknowledge in the preface to "Process and Reality"? (If the question is unanswerable, say "unanswerable")
William James and John Dewey