I'm not sure whether this is Amaranthus cruentus or A. hypochondriacus, since I no longer have the seed packet from two years ago. It re-seeded itself, and it grows well in the really poor soil on the south side of my house. It gets so big that it collapses in the fall, so next year I think I'm going to grow it along the chain link fence, where I can inconspicuously tie it up.
Killerplants.com has nice introduction to amaranth called "Why Were Amaranths Forbidden?"
I found a link to some interesting amaranth grain recipes - sadly, the only thing I've actually made from harvested & "popped" grain is a kind of rice-krispie treat-like confection.