Not sure how to get it down to five...this list would probably change hourly!
Cryptonomicon, Neal Stephenson (could pick any of his, pretty much)
Forty Signs Of Rain, Kim Stanley Robinson (ditto)
Black Man, Richard Morgan (ditto - but that is the best)
Memory, Lois McMaster Bujold (ditto)
Gaudy Night, Dorothy Sayers (or any Wimsey book)
American Gods, Neil Gaiman
Infinite Jest, David Foster Wallace
That's already seven, and I haven't mentioned Banks or Vinge or Flashman or Jonathan Strange or Charlie Mortdecai or...