We all know Mucha was a fantastic draftsman, but these little designs hammer home the point. And look what the guy could do with just a pencil and some white pigment! The image above was found on the Mucha Foundation website, which has a nice little collection.
For a more extensive pool of images, check out the Art Renewal Center. In fact, check out the Art Renewal Center even if you are not interested in Mucha. There is an extensive list of artists with articles and often VERY high resolution images, which can be sorted by quality, title, date, museum, medium, etc. A pretty cool resource. I'm a fan of the Bouguereau section (which contains over 200 images!), and the Gerome section (because duh!) - I'm telling you, the high res images are incredible.