Check this out! (Link via Jake Stratton-Kent forever ago. Before the anti-social network trend began...)
Follow that up with Ogden's Greek and Roman Necromancy, JSK's Geosophia (vol. 1 & 2), and his True Grimoire.
EDIT: Being upfront, the Necromancy sources link was written in response to the Witch of Forest Grove's Shaman comments way back when, since Greek and Roman necromancy have a pretty obviously solid aspect of blood sacrifice to them. She's since seem to have improved her stance, and I dig that. I won't bash her or anything over that.
Themis is also cool, if somewhat untrustworthy due to the author's unrelenting Victorian-ness. Still, how much do I like some of the awesome source material and comparisons? Very much so. There's so much information on the Agathos-Daimon/Agathoi-Daimones in there!
SECOND EDIT: This popped up during a cursory drift. I'm enjoy the introduction already, at least.
THIRD EDIT: You know? I'm in total asshole mode today. So I'm toning myself down by eleven notches. My apologies. A shitty driver pissed me off earlier and it seems to have stuck for longer than I should've allowed.