Frank's storytelling is rock-solid, so if you're looking for more work to study I'd recommend checking out some European artists.
European graphic novels are published yearly, not monthly and so the artists have a much longer time to invest. Generally the anatomy, layout, acting and story-telling are top notch.
You can google these guys: Benoit Springer, Enrico Marini, Juanjo Gardino.
Some western artists: Michael Lark, Alan Davis, Jose-Luis Garcia-Lopez (I'd recommend pre-1985 work), Stuart Immonen.
Mignola is great too (I saw someone suggest him) but kind of idiosyncratic.
And some Japanese: Hiroake Samura, Katsuhiro Otomo, Masamune Shirow (particularly Appleseed 3&4 and Ghost in the Shell 1)
If you're committed to study, you need to look past style, and surface level flourishes and really digest the nuts and bolts of the work.
Good luck!