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>>28582 for Hector,
You definitely can find such "darker" angels in games like In Nomine, Everlasting (Book of Light) and d20 Anger of Angels - not to mention Pandemonium, where the angels look and behave like Lovecraftian horrors! But I for one would like to see more of the good, bright side, to balance all the darkness and evil.
As to ghosts, this explanation doesn't hold. Ghosts have so much potential, but still there are very few good sourcebooks about them, comparing, say, to vampires. Pity!