Wow, there are so many great sprites here! Anyway, I'm going to give my two cents on some of them.
Wyverii, that looks amazing. It really does look like a Pokemon sprite, the coloring is fantastic, and that pose is really cool. I would definitely be scared if I was facing that thing in battle. Great all around.
Chaoscrippler has another of my favorite submissions. That pose looks great, and I also like the coloring a lot. I also like the shiny sprite a lot better than some of the pink ones that have popped up.
DougJustDoug, I really like your pose, but the area where the heads are feels a little crowded. Maybe you could change it up a bit, where one or two heads are in a different spot? Just a minor nitpick - other than that, great sprite.
KoA, on your frontal drawing, all the heads look pretty much the same, which I have a bit of a problem with. "Twinning," as I like to call it, or heads on a multiheaded beast that look the same, doesn't look that great in the long run. However, the back drawing looks great.
Atryoki, I agree with the others in that it looks a bit small, and the twinning problem exists again (the left and middle heads). I like where you're going, but it could still use some work.
I can't see aragornbird's sprite on my school computer for some reason, so I'll give some feedback when I get home.