I'm not a big fan of fanfic, but I am quite enamored of appropriations of pop culture that shed surprising new light on their source material.
For some time, my favorite example of this sort of thing has been Garfield Minus Garfield. By removing the titular cat from each comic strip, Dan Walsh exposed "the existential angst of a certain young Mr. Jon Arbuckle."

Garfield creator Jim Davis liked the idea so much that he agreed to do an official Garfield Minus Garfield book. I wonder if they sell it at the school book fair.
But I may have to choose a new favorite after discovering Peanuts, by Charles Bukowski, a set of short-story and poem retellings of classic Peanuts scenes as if they were written by the famous twentieth-century poet. In addition to the stories and poems, the series also includes re-titled Peanuts comic strips.

I'm a huge fan of Bukowski, I've written about his work, and I also loathe Peanuts, so this is perfect for me. The poetry is the best, of course, and the creator (I'm not sure who it is; the site is signed "Hanstock.") really nails the cadence, line breaks, and word choice of good old Buk. Here's my favorite one:
answers that never arriveI sit by the window and listen to the rain
come down
and I think about why we
do these thingswe sit with our elbows on these
brick walls,
talking
bickering
lamenting the passing of our youth,
and what it means to be
young.we write letters to Santa Claus
tell him about how
we’ve been good
we should get presents
waiting for answers that never arrive.we spend our days and nights
drinking
screwing
screaming our heads off
and all it ever really does
is make my stomach
hurt
