"Color and Light: A Guide for the Realist Painter" by James Gurney.
I've mentioned both this book and James Gurney on my blog before, but I cannot stress how useful this book is. If you are any sort of painter, or have to work with color at all, maybe you are in the lighting or cinematography department, then this book is worth more than 4 years in art school. If you only buy 1 art book in the next year, make it this one. Also, if you buy it on his website, he will sign it for you!
"Making Comics" by Scott McCloud.
I read this book in middle school and am still learning things from it 10 years later. Not just for comics, this book touches on composition, character, environments, writing and so much more. I think I might have become an environment artist because of this book, because he always encouraged drawing outside of your comfort zone.
"The Skillful Huntsman: Visual Development of a Grimm Tale at Art Center College of Design" by Khang Le, Mike Yamada, Felix Yoon and Scott Robertson.
Produced as a senior thesis project at Art Center College of Design in Pasadena, this book takes you on the entire design process for this project, from character silhouettes, to environment studies, to props, to finished art. There is a running commentary from the artists too and they discuss many helpful tips and tricks there. This has been a big inspiration for me, and helped me learn how to do concept art.
-CGSociety: A good resource for looking at art, talking to other artists on forums and keeping up to date on CG news. Although the culture of the website has gotten a bit exclusive in the last few years, I still check back every once and a while. Their work in progress forums are particularly helpful.
-Mayang Textures: I use this website all the time for finding high-quality photo textures for free.