Arthur Charles Fox-Davies (1871-1928) is one of the most prominent heraldic authors. Because his books are widely available, they are often used by SCA heralds. He focuses primarily on English heraldry.
While some of the text in his books have become dated, they remain some of the most thorough and informative heraldic books available. A Complete Guide to Heraldry is (at least amongst SCA heralds) one of his most popular works.