MusRef is an online database of print and online music reference sources, including thematic catalogs. Use the Simple Search feature to search for a composer's surname and the category "Composer Thematic Catalogue-Bibliography."
Directory site of links for research on a wide variety of topics in music, including historical musicology, ethnomusicology, music theory, composition, and performance practice.
DRM provides links to substantial open-access projects of use to musicians and musicologists. Search for "thematic catalog" or expand the "Structured Databases" section for online thematic catalogs.
