One great example of this is the Death Star run in A New Hope. Just before it explodes, it sounds just like the end of Mars Bringer of War.
Compare 6:56 -
Gustav Holst - The Planets - Mars, the Bringer of War - YouTube
to 8:07
Star Wars Episode IV Soundtrack - The Battle of Yavin - YouTube
There are also many more subtle Planets bits, such as the brief little quote from Saturn, Bringer of Old Age, to bring Holstian tragedy to the Destruction of Alderaan (more of an orchestration thing, this than an actual melody rip); a structural device - again, rather than an actual melody - from Venus is used as the robots' pod falls to Tatooine, a long descending run of notes over a stable chord ending on a shift up of the chord by one semitone for the last note, the effect of which, as in Venus, is one of warmth and grandeur. There are bits of Mercury and Jupiter in the running around the DS and the escape therefrom.
I think it highly appropriate that SW makes such use of Holst, not least because of the connection to myth they share ( though Holst insisted The Planets was about astrology, yes,
astrology, and not mythic figures). Artistically, I have no problem with Williams' Holst steals. But I'm a bit - and only a
bit, mind - uncomfortable with Williams receiving total credit for every note we hear in that score.
And yes, Sibelius is appropriate for LOTR too. I suppose my interest in having these rips pointed out is that we - and the world's viciously proprietorial copyright owners - understand what we're listening to. For instance the soundtrack of LOTR, including the Sibelius phrase, is copyrighted material, but no way in hell should that phrase become the intellectual property of the owners of that score. In short, in such a clear case as the Sibelius, a way should be found to give the classical composer a credit. In SW, though, the Holst lifts are more indirect, and a credit to Holst would be too cumbersome...hmm, where to draw the line...