This list is not a comprehensive list.
If anyone knows of other sources, please PM me and I will add them to the list.

Devon Family History Society
https://www.devonfhs.org.uk/

Genuki
https://www.genuki.org.uk/big/eng/DEV

FreeCEN
https://www.freecen.org.uk/
1841 - 100% transcribed
1851 - 45.7% transcribed
1861 - 100% transcribed
1871 - none as yet
1881 - just over 2% (but fully available for free on FamilySearch)
1891 - 100% transcribed

FreeREG
https://www.freereg.org.uk/
Check for individual parishes and coverage.

Findmypast
have transcriptions for
Devon Banns
Devon Baptisms
Devon Burials
Devon Marriages
Check the parish list (bottom right of page) for coverage of parishes.

They also have a Devon, Parish Registers Browse set, which means you can select a parish register and then look at the pages. Again, check the parish list for coverage, and note that although the dates might say (for example) 1663-1980, the register for 1794-1813 might be missing. (Usually because it's not available at the county archives.)

I'll list some more datasets when I have a little more time.

Other marriages
I recently found some people from Devon marrying in St Helier, Jersey, Channel Islands. Those marriages were found in Ancestry's Jersey, Church of England Marriages, 1754-194.

PLACES

Exeter
Dissenters' Graveyard

In use between 1748 and 1854. Noted from a post by FM varnie99.
https://www.edgt.org.uk/index.html