I was curious to know if there are any resources, books, blogs that focus on perfecting object shadowing and lighting with Photoshop and/or Illustrator? I have and know how to do basic shadowing and lighting but it is an area I know I need to improve and I would like to know some resources I can review or hopefully learn from. Studies are welcome, too.
I feel that lighting/shadow really do make up the most of an illustration - anyone can draw a square in Photoshop, so I found out two things that were very good towards improving my skills:
This might be a little aside, but I feel this might be an interesting addendum to your Q.
Here is an interesting thing.
This might seem silly-obvious, but it is a pretty big mental leap. I think why digitally created shadows often look a little weird is because of this. You choose light sources, intensity, angle etc. and you need an extremely well developed idea of light, refraction, texture, angles, intensity etc.
Way back when I went to art school we did a very interesting experiment. The object was, in this case, a badger skull we had (skulls are great practice):
So, the difference between drawing light and drawing shadows was surprisingly tough. To see the gradients of shadows and replicate this is reasonably easy. To see the gradients of light: not so simple. I suppose this is a very deep study of negative space.
This might not seem wildly relevant to your Q, but I am trying to point out the way we see things: you do not only need to see shadows, but on a fundamental level, you need to see light also. An ability to see light is actually quite tough to develop, but I believe a lack of this often results in not-very-elegant digital images. We almost seem hard-wired to focus on shadows. After all, we use shadows to determine the shapes of things, the depth of field around us.
If you are not working with 3d (such as in illustrator) where you choose light sources, this is still relevant.
Drawing with light, 3D: (an experiment I did in Maya)
Drawing with light, 2D: (my brain)
Drawing with shadow and a little bit of light (an experiment I did, bobcat skull) (The trick here is to determine what is between the beginning of shadow and the beginning of light. I.e., where is the threshold where the coloured paper alone IS the shape/texture. The parts where you do not draw light or shadow). It is hard to explain, but I hope you got something out of this :-S