Last year I picked up a copy of 'A Christmas Cthulhu' by David Griffiths and I really enjoyed it. I'm reading it again right now in fact, to get into the Creepmas spirit.
It's 'A Christmas Carol' steeped in Cthulhu mythos and done quite well I might add. There is also a Lovecraft inspired version of Dickens' 'The Haunted Man and the Ghost's Bargain' called 'The Haunted Man and the Reanimator's Bargain' and a short glossary in the back if you need to brush up on your mythos terminology.
Another book I thoroughly enjoy is 'Santa Claws' by Laura Leuck and illustrated by Gris Grimly. I'm a huge fan of Mr. Grimly's artwork. The story is a fun read and the characters are awesome. It's also chock full of Creepmas décor ideas and festive holiday dishes, like poison berry pie, cookies topped with flies and eggnog with spider legs.
This weekend I made chocolate chip cookies, with the sole purpose of making cookies topped with flies. I've seen spider cookies where they just dragged a toothpick through the melted chips to make legs. I thought I could do something similar, but fly wing shaped. It didn't work out like that. If I try again, I'll try piping on some melted chocolate in a fly shape. I also got eggnog. I thought I'd sprinkle on some chocolate jimmies and call them spider legs. Nobody wanted fake spider legs in their eggnog. Maybe I should have just bought a cherry pie, said it was poison berry and called it a day.
Another one we read every year is 'The Nightmare Before Christmas' by Tim Burton. I'm probably in the minority, but while I like both the book and the movie, I prefer the book. Like 'Santa Claws', it's fun to read aloud, the artwork is gorgeous and full of Creepmas inspiration.
Then there is the classic (classic used to mean old stuff, now it means things that have been around since I was a kid), 'How the Grinch Stole Christmas', by Dr Suess. This one is fun to read too, but unless you sound like Boris Karloff, it pales in comparison to the cartoon and the book doesn't have a theme song.
Finally I'll end with M. R. James. If you'll be telling scary ghost stories and tales of the glories of Christmases long, long ago, you'll need a little M. R. James. At Thin-Ghost.org you can read all his ghost stories.