I'm looking for public databases containing data about the works of different composers, just like the Köchel catalogue. I'm not really interested in any particular artist, genre, or time period. Instead, I'd rather like to know where to look for data like that in general. Pointers to explicit lists are nevertheless welcome.
Wikipedia has a category of music catalog pages.
Here are a few links I found to complete lists.
The best, and always most up to date, place to go for complete works catalogues is the Grove Dictionary of Music and Musicians. It is available online, but you must have access to a subscription of some sort. Many universities and public libraries have online database subscriptions.
Grove allows you to search by composer. Each entry includes a complete biographical history, a complete works list, and bibliography of places to go for even more information.
If you are then interested in finding the music listed, the complete works list also includes excellent bibliographic information of all scholarly editions in current publication.
The Bach-Werke-Verzeichnis (Bach Works Catalogue) is the numbering system identifying compositions by Johann Sebastian Bach. The prefix BWV, followed by the work's number, is the shorthand identification for Bach's compositions. The works are grouped thematically, not chronologically.