Grimoire.org – the grimoire encyclopedia, with an extensive list of grimoires, links to online and purchasable versions, the major changes and timelines related to each one, and an extensive demonology with text references and spell list.
The Grand Grimoire – “Don’t try this at home.” The Grand Grimoire (AKA the Red Dragon Grimoire) is a pretty solid example of a necromantic spellbook. Highlights include conversations between demons and the summoner, creating a pact, and extensive et cetera. This is, to be clear, some dark magic, but if you’re looking for a sense of the ceremonies and goals of necromantic magic, this is a good resource. Possibly somewhat sensationalized though.