(a deliberately short list)
Peter Sturrock (Stanford University physics professor)
J. Allen Hynek (Reprint of a classic book by the late Northwestern Univ. astronomy professor and Air Force consultant)
Richard F. Haines (retired NASA psychologist)
WARNING: The cover of this book shows the standard model gray alien (that's a particle physics -- also cosmology -- joke). Remember the old maxim though: Don't judge a book by its cover. But you might want to have this one shipped to your home instead of your office.