Don't know if anyone's mentioned it, but you'll find graphic novel adaptations of "At The Mountains Of Madness" and "A Princess Of Mars" as well as other classics here:
I've seen both at the local Barnes and Nobles, and have flipped through them. I will take this version of Mars over the IDW stuff any day. It appears to be the most faithful version so far, and looks closer to what would've been done then, what with Dejah Thoris looking somewhat Egyptian. And yes, she's naked throughout the book. The art style is simple, but elegant.
"At The Mountains Of Madness" has a somewhat cartoon like quality, yet it too is of the simple and elegant kind. And like "A Princess Of Mars", it is very faithful to the source material.
It looks like they all have the same artist, which is amazing given the differences in style between just these two books....I'm amazed at how this person was able to churn out several graphic novels, but there it is.
At any rate, I plan on picking these two up in the near future.