(I covered Stockhausen and Mauricia Kagel's contributions to Beethoven ephemera HERE).
Luc Ferrari, who likes to juxtapose natural environmental sounds with noise/sound effects, said in a relatively recent interview in Paris TransAtlantic that, were he imprisoned in his studio for the rest of his life, he'd request to have Beethoven's Opus 106 remain with him (the Hammerklavier piano sonata).
Here's Luc Ferrari's "Strathoven": (the title will become self-explanatory...)
Gyorgy Ligeti also loved Beethoven, at least as a child. Speaking about how he learned to compose: "I had a kind of game which I played. Going to school took less than twenty minutes on foot and I always imagined... it was some Beethoven symphony or Schumann... what I heard from the radio and... of course, Beethoven was the centre. And, I always imagined I listened to a concert, I imagined this music naively and I heard it. And from this kind of listening to inner fantasy, which were not original, which were full with influence"
Here are 2 pieces by Ligeti, one a piano piece which sounds like it might have had its seeds sown from listening to early Beethoven piano sonatas, and another work which is probably closer to "sound effects" than anything using sonata-allegro form...
Musica Ricercata III (Béla Bartók in memoriam)(1953):
Pierre Henry is another composer who works almost exclusively in musique concrete and electronically generated sounds. He wrote quite alot about Beethoven in the liner notes to his homage and "remix" of Beethoven's "10th" symphony... I previously posted the liner notes HERE.
I decided to make a little visual accompaniment to the samples off of Amazon's page:
Finally, Helmut Lachenmann, another very modern composer (who at least one blogger thinks could be today's Beethoven), spoke about how he hears Beethoven "afire with his energies as a composer" during the Eroica Funeral March... He also composed "Staub" (1987) which is supposedly based on Beethoven's 9th symphony and is designed to precede a performance of the 9th. No video to be found, sorry...
Here's "Gran Torso", probably his most famous string quartet work. Tho very interesting, I think it's safe to say it wasn't derived from a Beethoven work.