Today: Angels and Demons.
Firstly, Angels and Demons at monstrous.com gives a quite detailed look, both historical and mythical, at the nature of demons and angels.

Here's the soc.jewish.culture FAQ on the mattter.

Alan Moore and J.H. Williams III's Promethea Book 3 gets into the "reality" behind angels and demons; the annotation for the revelant section for this wonderous text on magical thought is found here.

Promethea herself being damn sexy, one might be inclined to think about sex and the single celestial. Most of the Angel or demon related erotica I've read is rather... hmmm... predictably shallow or pretenious... so let's see about creatng our own. Do your part and summon a succubus or incubus today.

Alternately (and almost as much of a heresy), you can envoke, invoke, and provoke angels for use in spells. Hint: He-Who-Is-Like-God don't do light beers. Give Mikey full larger! Oh, and he loves the rain.

Do you realize how often Sailor Moon uses Angel imagery?

Finally, the indescribably wrong in all the right right ways gives us an RPG transcript...