This article is from the Pratchett Newsgroups FAQ, by Orin Thomas email@example.com with numerous contributions by others.
P.G. Wodehouse, Douglas Adams, Jerome K. Jerome, Robert Rankin, Tom
Sharpe, Tom Holt, Calvin Trillin, P.J O'Rourke and Dave Barry are some
people whose styles are similar. He reminds me a bit of Joseph Heller
(Catch 22) as well ... although not so cynical.
Terry occasionally also posts information about books that interest
him or have impressed him recently. Keep a look out on alt.fan.pratchett