Mine might be Kim Stanley Robinson's Mars trilogy (not one book, of course). I don't know that it's the most enjoyable one I've ever read, but it's the most astounding one that comes readily to mind.
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Anonymous2008-05-15 8:05
If you count The Little Prince, probably that. If not, but you count some of William Burroughs' books, then those.
Otherwise, I second Stranger in a Strange Land, with VALIS as a second-choice.