From a discussion on the 30-Violins Club web-board, I list some cross-over music which failed to acknowledge the sources of their arrangements, to my knowledge and memory, in no particular order:
Andrew Lloyd Webber, Variations 1-5
Taken from Rachmaninov, who in turn took it from Paganini’s 24th violin caprice. Apparently in his patent, Lord Lloyd Webber also stipulated that no one else could make a new arrangement of the classical work without infringing his copyright.
Yanni at the Acropolis, Aria
This was taken note-for-note from Delibes’s Flower Duet.
Vanessa-Mae, music video of Storm
Vivaldi’s Summer (3rd movement) with a drum-beat and MTV. Though since Vanessa-Mae has acknowledged use of classical composers in other works, this is likely to be an omission from the video people.
I also suspect that the original theme from Batman was influenced by the opening theme of Schubert’s Unfinished Symphony... but then Danny Elfman has contributed so much to original work that he deserves the benefit of the doubt.