Writers of the Future is probably the biggest one, but you probably already know about it. I think it's more geared for science fiction, but they also take fantasy on ocassion.
Beyond that, I don't really know of any. I recently placed in a first chapter competition for the sf&f literary magazine at my university, though! Their next issue has an art-related contest, so maybe that's worth checking out.
I have yet to do it as winning awards isn't high on my list of goals. Also it might be because I don't feel like coughing up the fees either. But they do seem to be fairly serious about what they do. The emails I get are loaded with red carpet style award show photos. It might be worth a look to see if what they offer is what you're looking for.
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