I heard about the contest waaay late, but managed to churn this guy out in a couple days.
I went with the theme of nature reclaiming the earth. Instead of post-apocalyptic over-growth or vast storm desolation, I just decided that mother nature would conjure up a horde of organic mutants-- comprised of the earth itself-- and wipe man off the face of the planet.
Photoshop CS3, sketchbook and Rusty, my beat up intuos 3 tablet.
Thanks for looking!