List from Genealogy Gems:
Selected list of major online Catholic Church parish records:
United States:
Diocese of Baltimore (MD) – Findmypast ($)
Diocese of Boston (MA) - American Ancestors ($)
Diocese of Chicago (IL) – FamilySearch.org and Findmypast ($)
Diocese of Cincinnati (OH) – Findmypast ($)
Diocese of Fort Wayne-South Bend (IN) – FamilySearch.org
Diocese of New York City (NY) – Findmypast ($)
Diocese of Philadelphia (PA) – Findmypast ($)
Diocese of Springfield (IL) – Ancestry.com ($)
Diocese of Toledo (OH) – FamilySearch.org and Findmypast ($)
United Kingdom
England – Dioceses of Birmingham, Liverpool, Middlesbrough, Plymouth, Salford, Southwark, and Westminster – Findmypast ($)
Scotland – Dioceses of Aberdeen, Argyll & The Isles, Dunkeld, Galloway, Glasgow, Motherwell, Paisley, and St Andrews & Edinburgh – Findmypast ($)
Europe
Austria – Matricula (browse only); https://data.matricula-online.eu/en/
Belgium – State Archives of Belgium (browse only); https://search.arch.be/en/themas/tips/507-church-registers-en
Germany – Matricula (browse only); https://data.matricula-online.eu/en/
Ireland – National Library of Ireland (browse only): https://registers.nli.ie/; Indexed on Ancestry.com ($) and Findmypast ($)
Italy – FamilySearch.org
Luxembourg – FamilySearch.org
Slovenia – Matricula (browse only); https://data.matricula-online.eu/en/
Spain – FamilySearch.org; Ancestry.com ($) and MyHeritage ($)
Mexico, Central and South America
Mexico – FamilySearch.org and Ancestry.com ($)
Haiti – Archdiocese of Port-au-Prince – FamilySearch.org
Peru – FamilySearch.org
Some other countries – FamilySearch.org
Asia:
Philippines – FamilySearch.org