All time:
Guards Guards by Pratchett or Brightonomicon by Rankin
Runners up places go to the Death Trilogy by Pratchett or Witches of Chiswick by Rankin
Worthy mentions:
Angel & Demons + Davinci Code, LOTR, Hobbit, Rats/Lair/Domain, The Stand, Fox in Socks + countless others I don't have time to mention.








