A prosopography of ecclesiastics and lay people active in sub-Roman Britain, with biographical details and full citations and bibliographical innformation, as well as cross-referencing,
For what it does, this is the best you can ask for. This is a complete compendium of every saint in the British Isles before 700. Every tidbit of information to be found is here. The only issue with this volume is that the editor, John Morris, kept inputting his own reasoning over the source material. That can get confusing at times but the confusion is well worth the rewards this volume provides.