I've never seen anyone say it, but it always seemed to me that the ending of Donnie Darko was curiously similar to the ending of the Polish director Krzysztof Kieślowski's 1993 film Blue. Now, thanks to the wonders of YouTube, I can show you how! Here is Donnie Darko's ending:
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And here, Blue's (the part I'm talking about is 1.40 in):
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Directors steal stuff from earlier films all the time. They're allowed to call their stealing 'a homage' when the audience might conceivably be aware of the original source. Since I'm sure many viewers of Donnie Darko have seen Blue and appreciate the reference, this is obviously a homage.