Hi there, nice to see another Donaldson fan on the boards.
I've read all of the T. Covenant books previously as well as Book 1 Runes Of The Earth of what will be the final quartet. I mention this latter fact in case you weren't aware of that fact and would therefore wish to know.
Certianly a landmark series in fantasy IMO.
I and certainly other members can probably track down artists who've done Covenant artwork but in the meantime here's Donaldson's web site in case you don't have it.
There'll have been several publications of this series over the years, which means several book cover illustrations and probably more pictures. http://www.stephenrdonaldson.com/