The Necronomicon. A legendary collection of the most mind-shattering magical secrets known to man, and one of the holy grail props of both horror and Cthulhu mythos fans alike. If you're looking to craft an excerpt from that forbidden tome this collection of Necronomicon Brushes for Photoshop by ~DarkNova666 on DeviantART should be a huge help. Here's a sampling of what it includes:
The full set has about two dozen different occult symbols and should be compatible with any image editing program that can import brush files.