In no particular order:
The Hitchhiker's Guide to the Galaxy: This is what I read at the age most geeks I knew were reading Tolkien. There's the obvious comedy veneer to the narrative, but underneath is fairly meaty philosophy. Story in short: Arthur Dent gets his house demolished to make way for a highway bypass, only to find himself lost in the Galaxy when, in a cruel twist of some form of irony, his planet is destroyed to make way for an interstellar bypass. Hilarity ensues.
Jurassic Park: Dinosaurs, eating people, in a zoo setting? Wuwu~! Sure, I picked it up mere months before the film release; I was twelve, so sue me. Still a fun, fun read.
Calvin and Hobbes and The Far Side collections: I blame my father (for the former) and grandmother (for the latter). Who gives an eight-year-old such subversive materials, really? Accounts for my philosophic bent today, I suppose.
Cruel Shoes: Come for the titular story, stay for "The Day the Dopes Came Over" and "How to Fold Soup." (Hmm, again with the satire; methinks there's a trend ...)
Stuart Little: Okay, it's a kids' book. It's also a rather endearing tale, about growing up different and still finding one's place in the world.