I've gotten a couple of requests in the comments to share about my process and what mediums I use in my work. So while I have a few little bits I need to keep to myself, I thought I'd share most everything else:
First off, I do all my sketching on tissue paper. Because I don't consider myself an excellent drawer, I find tissue paper easiest to work with... making a few initial drawings and then choosing bits and pieces of each and piecing them together by overlaying the paper. This also makes for some built in mistakes and odd perspectives, which I think makes the work more interesting. This also means that I don't have a formal "sketch book" where I draw out all my ideas. It's all loose papers, and I tend to throw them all away after a job is done because 1) I don't want a bunch of clutter in my studio, and 2) because I don't really care about all the physical sketches that lead up to a finished piece of work. (They are saved digitally anyway.)
After I get approval on a sketch direction, I start painting. I use simple acrylic paints. I like Liquitex from the art supply store. They mix well to make good custom colors and the consistency is nice too. I usually just use a handful of colors and mix... unbleached titanium, cadmium red, neutral gray, cerulean blue, etc. I paint out everything on paper as well. I really like Hahnemuhle paper, but I've been out of that for a while, so I just use whatever's laying around. Usually a sketch book page ripped out.
The brushes I use have been collected over the years. So they are kind of mixed and matched, but usually pretty good quality. (Cheapy kids brushes fall apart after a few uses.) I use a few small tipped watercolor brushes for fine details and a bunch of big flat brushes for flat color blocks.
My favorite brush that is used most often is a flat Grumbacher with a plastic handle. This is good because the bristles have held up well over the years, and I can forget about it for days in the water jar and the handle doesn't fall off.
I then do my linework (or typography depending on the assignment) on another separate sheet of paper. Sometimes in ink -- typography is good and clear in ink. But linework for paintings is more often done as a monoprint that gives me rough textures and organic mistakes (I call it grunge) here and there.
I then take all the parts and pieces and scan them into photoshop using a Canon Canoscan 8800F. Then compile it all digitally, creating a final piece that I can easily send off to the art director via email or ftp. I used to work all on paper, creating one final physical piece, but I've found that it's much easier to change and revise things when it's digital. And I can easily adjust color if it's not feeling right. Or I can play with placement or off-setting the elements a little more if it didn't quite come out the way I'd envisioned in on paper. I work really fast on the computer too, which helps me be more prolific.
I don't use a wacom tablet or digital color in photoshop because I like the hand-made quality to real paint. And I never quite got used to drawing with a wacom, unfortunately (that might have saved some paper I suppose).
After the job is completed and approved by the art director, I toss all the parts and pieces and prelimary work into the recycle bin and start the whole process over on the next job.
I hope that helps! If you have questions, please leave a comment and I'll try to answer there too.