I have loved Jim Lee's work on comics for a long time now and have found that there are quite a few vids of him doing sketches drawings, inks and more on youtube for us all to see. We get to see his finished works of course, but it is all the more inspiring to watch his pieces actually come into being.
[Some Jim Lee covers from his ComicDB entry]
He has a nice big entry in ComicBookDB and indeed the Cover Gallery therein.
Here are a few of the vids I like - these are multi-parters, so there is plenty here to admire after you are drawn in by these first parts: