Church records for some of the Bistumarchiv of Trier are now online at ARCHION: https://www.archion.de/de/alle-archive/rheinland-pfalz/bistumsarchiv-trier
Bestand original Kirchenbücher in Brühl with links to registers: https://www.wgff.de/aachen/download/LAV_NRW_Bestand_Original-Kirchenbuecher_ehem_PSA_Bruehl.pdf
Time Machine for Koeln has large database taken from church and other records: Link to database
Link to digitized bild archive in Koeln (Cologne) : http://historischesarchivkoeln.de/lav/index.php
See Ancestry.com Collections.
Military church books for Köln are available on Matricula: http://scope.staatsarchiv.sg.ch/archivplansuche.aspx?id=778314
Evangelical church records: https://www.evangelisch-im-saarland.de/Kirchenkreise
Link to digital archives of Cologne: Erzbistum-koeln.de/