Eww, demon porn.

Assanine jokes aside, I spy wif' me lil beaner eyes an issue with the anatomy. Of the blue demon's, to be exact. I guess you could say thats the way he's supposed to be built, but I just don't think it fits him.
First and foremost, his abdominal region seems off in my opinion. His left Pectoral muscle seems to be painted on to his chest, much like stretched t-shirt and seem to be out of line with the right pectoral, as are his obliques. I would try and shorten the left pectoral by moving the part where the pec' meets the shoulder further back left, and draw the arm pit. As for the obliques(or ribs, or whatever it is depicted underneath his left pec) they should be less parralell with each other, and shouldn't be drawn out that far.( imo, they look like they are bieng drawn out all the way to his back) Also, his six pack travels all the way down to his third knee( third knee you ask? The Wee "knee" of course!). I think that it would look a lot neater, by getting rid of the lowest set of abdominals, or just scrunching them up a bit. Also, with such a big upper body, he seems to have a deficient set of arms. Very puny lookin' if you ask me...and ditto what Mirre said about the pose of the hand and trident.
Aside from the obvious crits though, your style seems to outshine these small flaws. I also agree that the red demon is very sexay'. And you got some good beginnings with the blue devil creature, as I like the pose, and the style of shading.(would be keen for some more demonic teeth though)...Great job though, me likey lots!
***EDIT 10/18/06***I just got in from work and made a quick edit of your work, Trem (hope you don't mind). I'm not very well versed at describing issues I see as some people are, such as Helm, Ptoing, and Pawige. I think the best way for me to describe this issue is by pixeling it for you. Below is my edited version of your blue demon. I might have accidentally killed your style and blended it a bit with mine( sorry!):

I made the following changes: the upper body, the pectorals, buffed up his arms to match his large upper body, extended his left foot a wee bit, added some detail to the trident, changed his head and gave him a bit of snout from a different angle with a different set of teeth. I decided to leave the leg length alone, as I thought that was the intended look...Hope I helped you out!