I find that at libraries and bookstores, I spend less time in the Art sections these days, and more time in odd reference topics, such as fashion, antiques, architecture, etc. I don't need a tenth "how to draw human anatomy" book, I need books on the flavor of human existence.
Here's some studies of illustrations in Cally Blackman's 100 Years of Fashion Illustration. I tried to name the dudes I was drawing from, but where my notation failed doublecheck the book. Good read! Also, random art theory note: People often have trouble wrapping their heads around Andy Warhol, and his ideas about multiples, mass production and pop art. Knowing he got his start in fashion illustration, it makes a lot more sense. Fashion deals a lot more with repeating textiles, and one "art piece" of a dress is designed for it to be worn by lots of people. In essence, he was applying the motives of fashion to visual art, where you normally make a singular unique painting, and that's where its value comes from.