One of the challenges that become more apparent as the Steampunk and Dieselpunk genre begin to mature, is finding art that is able to delinate the line between Steampunk's Art Nouveau style and Dieselpunk's Art Deco. There are those who, for whatever reason, confuse the two - which is unfortunate, because though I do enjoy Art Nouveau, I also have an eye for Deco. Parsing the line between the two is a challenge, but I would say the Mr. Stephen Crowe, an exceptionally talented illustrator from Wellington, New Zealand, has been able to hit the mark between what might be termed as Late Nouveau / Proto-Deco. Though there are the smooth and sharp curvatures of Art Deco in his illustrations, one can also see the 19th century stylings in the attire, along with added details to the designs.
I've not been able to find much more of his Steampunk work (well, aside from his outstanding vehicle illustrations on DA), but do pay a vist to his outstanding gallery, located at: http://stephencrowe.deviantart.com/, and http://www.stephencroweillustration.com/ - Do enjoy!