I trust you know Terry Pratchett? And of course Neil Gaiman? Imagine the two of them together.... The result is Good Omens: The nice and accurate prophecies of Agnes Nutter, Witch. An absolutely hysterical must read.
Pratchett (of Discworld fame) and Gaiman (of Sandman fame) may seem an unlikely combination, but the topic (Armageddon) of this fast-paced novel is old hat to both. Pratchett's wackiness collaborates with Gaiman's morbid humor; the result is a humanist delight to be savored and reread again and again. You see, there was a bit of a mixup when the Antichrist was born, due in part to the machinations of Crowley, who did not so much fall as saunter downwards, and in part to the mysterious ways as manifested in the form of a part-time rare book dealer, an angel named Aziraphale. Like top agents everywhere, they've long had more in common with each other than the sides they represent, or the conflict they are nominally engaged in. The only person who knows how it will all end is Agnes Nutter, a witch whose prophecies all come true, if one can only manage to decipher them. The minor characters along the way (Famine makes an appearance as diet crazes, no-calorie food and anorexia epidemics) are as much fun as the story as a whole, which adds up to one of those rare books which is enormous fun to read the first time, and the second time, and the third time... --This text refers to an out of print or unavailable edition of this title.
From Publishers Weekly
When a scatterbrained Satanist nun goofs up a baby-switching scheme and delivers the infant Antichrist to the wrong couple, it's just the beginning of the comic errors in the divine plan for Armageddon which this fast-paced novel by two British writers zanily details. Aziraphale, an angel who doubles as a rare-book dealer, and Crowley, a demon friend who's assigned to the same territory, like life on Earth too much to allow the long-planned war between Heaven and Hell to happen. They set out to find the Antichrist and avert Armageddon, on the way encountering the last living descendant of Agnes Nutter, Anathema, who's been deciphering accurate prophecies of the world's doom but is unaware she's living in the same town as the Antichrist, now a thoroughly human and normal 11-year-old named Adam. As the appointed day and hour approach, Aziraphale and Crowley blunder through seas of fire and rains of fish, and come across a misguided witch hunter, a middle-aged fortune teller and the Four Horsepersons of the Apocalypse. It's up to Adam in the neatly tied end, as his humanity prevails over the Divine Plan and earthly bungling. Some humor is strictly British, but most will appeal even to Americans "and other aliens."