The following is a list of full-text books relating to Devon which can be found on Google Books. If you know of any more do let us know.
Barnstaple parish register of baptisms, marriages and burials
by Thomas Wainwright
In addition some volumes of the Report and Transactions of the Devonshire Association for the Advancement of Science Literature and Art are now becoming available on Google Books, and no doubt more volumes will be added in due course.