The Hitchhiker's Guide to the Galaxy (series), by Douglas Adams (pub. 1979-92)
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This was originally a radio comedy, though I never heard that until some time after reading at least the first three books in the trilogy, I think. (There are at least five books in the trilogy.) But I think the first experience I ever had with the Hitchhiker's Guide was probably the TV series. Whatever, I eventually read all five books, and they became my favorite books ever. Of course, that was years before I ever started writing book reviews on my site, so eventually I had to reread them all, in order to finally write reviews. Meanwhile, I should say I once had a few vague ideas for writing a sixth book in the series, myself, but someone else has already done that. I haven't read it, but I should, someday. Oh, also, I have a section where I once put various entries of the fictional book-within-the-books (of the same name as the first book in the series). You might be able to find other, probably better versions of this idea elsewhere on the internet, but this is my attempt at it. (And someday I hope to put more entries in it, from the radio series, which I need to re-listen to.) Anyway, on with the reviews:

The Hitchhiker's Guide to the Galaxy
The Restaurant at the End of the Universe
Life, the Universe and Everything
So Long, and Thanks for All the Fish
Young Zaphod Plays It Safe
Mostly Harmless
And Another Thing... (by Eoin Colfer)
(Probably I'll also review "The Salmon of Doubt")