Kenneth W. Osbeck has written several hymn story books (CLICK HERE).
Other hymn story sites include:
Worship Map Resources: Hymn Story.
Great Hymn Stories
Hymn Stories
Short Stories About Great Hymn Writers
I sometimes consult Albert Christ-Janer et al., American Hymns Old and New, 2 vols. (Columbia UP, 1980; vol. 2 is "Notes and Biographies") and Armin Haeussler, The Story of Our Hymns: The Handbook to the Hymnal of the Evangelical and Reformed Church (Eden Publishing House, 1952). Very brief but sometimes informative notes are attached to each hymn in Maria Leiper and Henry W. Simon, A Treasury of Hymns (Cornerstone, 1968).
~Masato