Tsk tsk! How DARE you not have heard of Terry Pratchett <img src="/ubbthreads/images/graemlins/winkwink.gif" alt="" />.
I have 31 books: 26 novels, Science of Discworld 1, Nanny Ogg's Cookbook, The Last Hero and Good Omens (I am a Gaiman fan).
Started with Guards!Guards! and would reccomend everyone to start with this book.
As for humour, I'll let yourself to judge. I know no one's sense of humour is alike so I will keep silent <img src="/ubbthreads/images/graemlins/smile.gif" alt="" />.