"Bunnicula" was a book I must have read a million times when I was a kid, the tale of an intrepid dog, a paranoid, conspiracy-minded cat and a strange little rabbit that drained veggies dry.
It spawned several sequels and several other books in a related series, also being featured as an ABC cartoon special one Saturday morning. I remember seeing the animated version and blissing out as some of my favorite characters come to "life." That and the ABC Saturday adaptation of "The Trouble With Miss Switch," another of my favorite for-kids spooky tales, represented a real highlight of my young existence.
Bunnicula did more to shape my early character than just about any other book I read. More than Poe, more than Lovecraft, more than M.R. James, Ambrose Bierce and Algernon Blackwood, more than Robert Bloch, Clarke Ashton Smith and dozens of dozens of other "weird fiction" writers. Heck, I'm tempted to go buy the boxed set on Amazon right now.
If you have kids, it's a great read. If you don't, it's still a great read, chock full of enough humorous asides meant just for adults to be highly entertaining no matter how old you are.
I grew up next to a curious neighbor who had a fantastic (I never knew how much so until later) collection of arcana on a variety of paranormal topics. I remember going over to his house and asking if the book on vampirism that Chester used as his primary source was in his collection. He was rather amused, but alas -- the book is fiction, as far as I know. ;) Still, if anyone would have been able to produce a copy before a young boy's wondering eyes, Marvin was probably the best candidate.