The Hitchhiker's Guide to the Galaxy, and I mean the whole set of six stories, is quite possibly the best thing ever written! It is by far my favorite book! I have indoctrinated so many people into the Douglas Adams fan cult by simply lending out my copy.
The style of writing is remarkable - I don't know how he maintains it. It's completely an insane, quirky point of view but retains flow, rationality, and plot/character cohesiveness throughout. And mostly, it's just plain entertaining.
The first time I read it I laughed until I cried a dozen times and I read the whole set in two nights. Two nights! I got like zero sleep but it was just that incredible.
I have it all: the original BBC Radio shows, the original TV series and the books that followed (!) from that. I do even own the (not so good) movie.