Jasper Fforde! *swoon* Oh how I love Jasper ...

Also Robert Rankin, Tom Holt, HP Lovecraft, Kinky Friedman, Joseph Heller, George Orwell, Aldous Huxley ...
(looking back through old library records from when DS was 14!). Non-fiction but Ray Kurzweil is awesome, The Singularity is Near. Oscar Wilde is awesome too even though olde worlde smile

I also second Hitchhiker's Guide and Vonnegut and Gaiman.