I know this is quite an old thread, but this has always been my favourite depiction of Morgoth, Ted Nasmith's "Morgoth punishes Hśrin":
http://corecanvas.s3.amazonaws.com/t...al/silm_12.jpg
One of the best things about it in my opinion is that it leaves Morgoth's face to our imagination. I'm not such a fan of the face in Nasmith's front-on depiction which was posted above:
http://img-fan.theonering.net/~roloz...th/morgoth.jpg
My issues with certain fan depictions of the Enemy are as follows:
1) Too much plate armour. I know Morgoth was in his origin a great "maker" but nonetheless such armour to the best of our knowledge probably didn't exist at any point in Arda's history. Nasmith depicts Morgoth in mail and with a more "kingly" cloak and crown, which I think reflects Morgoth's character. I feel like he saw himself as a ruler more than a combatant.
2) Either covered faces or overly demonic or goblinoid faces - I think he should have a "terrible countenance" - hideous perhaps - but in the sense of a sneering, contemptuous, evil human being, full of arrogance and loathing for all other things.
I have the same problem with the depictions of balrogs that typically display them as horned and hoofed satyr-devils even though there's nothing in the text to substantiate this claim (and in my opinion they're more inspired by the fire-jötnar of the Norse).
Some of you may have seen before my own (rather crude) attempt to visualise Morgoth:
http://robanes.deviantart.com/art/Mo...ured-292036738
He's not haughty enough, however, in my opinion, and I wish I'd made him look less brooding and more angry. And given him eyes.
Here's Gothmog:
http://robanes.deviantart.com/art/Th...rogs-441388773
Apologies for shilling my own stuff but this is the closest I can come to conveying how I personally see these characters to some extent.