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If comics count, then there are the alien vs predator comics. I didn't read them, but they even spawned their own movies.
Most of the tie-ins are made for a very specific audience. But you must make good money with them, since so many of them exist.
Some of the warhammer 40k novels are quite good, if one likes military sf. I think Dan Abnett is the most well-known of their authors.
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