a few ideas...
-Hard Rock/Metal Album Cover (something that looks like it would go with something hardcore, band does not have to exist (could be a band in the future), but the heavy metal/hard rock genre must be obvious through the symbolism in cover art)(noticed Angel Intheuk already suggested something similar, but all the better reason to use as a topic)
-The First Encounter (depict the event of which humans first encounter life on or from another planet)
-The Punishment (could be based on a mythilogical event such as Prometheus or Loki or something different that depicts punishment in some way)
-The Climax (could be based on one of shakespeare's plays, or a turning point of some story, but it is an event of some major significance in some story, game, movie, w/e)
btw...just out of curiosity, when is the winner's gallery gonna be put up?