Good Omens by Neil Gaiman and Terry Practchett is one of my all time favorite books. Personally I consider it to be a work of genius.
A while ago I read a book called The Hounds of the Morrigan by Pat O'Shea which very much reminded me of Good Omens being quite similar in its sense of humor and story and it did with Irish Lore what Good Omens did for Armageddon.
So currently I am reading American Gods by Gaiman and its writing style also recalls Good Omens to my mind, it is in reading this book which led me to this.
Does anybody know of any other books which bare some similarity to Good Omens?