Books!! Since you say "anything really" I'll give you some I like. I found some really good anatomy books at my local library in the art section-look there. Also, I find concept art (from movies) to be really helpful and inspirational as well! One I really want to get is the concept art book for Rise of the guardians. I think it really helps to see other people's sketching/art processes.
;bulletblue: 3DTotal [link] - the same people who made Digital Painting Techniques series
LoveCastle [link] , FineartSK [link] , PoseManiacs [link] and pixelovely [link] all focuses on improving anatomy. They have photographs that can be used for references or a timed drawing exercises.
AnatomyArcade [link] is a game designed to help expand knowledge on anatomy.
Pose Master free [link] (YouTube link) is actually a software exactly like PoseManiacs but you don't need internet and you can change timers, use the pre-loaded photos and even use your own photos. (I know it's safe as I use it from time to time).
AnatomicalArt [link] and LearningAnatomy [link] are both Tumblr blogs focusing on anatomy tutorials and references.
D'artiste series by Ballistic Publishing - I have the concept art one in the series and it's very good. The downside is that they are very expensive. They have info on artists, artist galleries and tutorials. Each book focuses on one subject: Concept art, 3D modeling, Character design, fashion design etc... [link]
Digital Painting Techniques: Masters Collection series by 3DTotal - These are also very good. There are different volumes. They are like D'artiste but slightly cheaper. They have info on artists, tutorials and such. [link]
Fantasy Art Workshop: Mastering Digital Painting Techniques by ImagineFX [link]
Impeccable Scene Design for Game, Animation and Film: Scene Design Course by Weiye Yin - I find this book very useful when drawing landscapes - It does teach about digitally drawing landscapes but it also has the theory side of it as well. [link]
DRIVE: vehicle sketches and renderings by Scott Robertson - A book focusing on machinery and cars it has tons of sketches, concept art and 3D models. [link]
Bold Visions: The Digital Painting Bible for Fantasy and Science-Fiction Artists by Gary Tonge [link]
Here are some books that focuses on anatomy, poses and anatomy references
An Atlas of Anatomy for Artists by Fritz Schider [link]
The Figure: The Classic Approach to Drawing and Construction by Walt Reed - Walt Reed explains the human body in references simpler then Hogarth. It also focuses on poses. [link]
Book by Burne Hogarth - Although he draws the human body very muscular his techniques in creating the human body, putting it into poses and getting things in proportion etc... are very effective once understood. [link]