Being one of things most-asked when I meet folks in person, it seems a good topic to address here. What inspires me?
This can be answered from at least two angles: the practical and...it's hard to come up with the second word. I'll think about it as I move forward.
Practically speaking, every work I do is a problem-solving exercise. Given the size and proportions of a rectangle, the bullet points of narrative, idea or character that need to be included from the art order, graphic design elements that will overlay the art, it's my job to arrange these pieces in any of an infinite number of ways to create something attractive, interesting, etc..

Casting about for ideas is at once the most and least exciting aspect of any artwork. I find it incredibly exhausting to iterate on a concept. It's like wringing water from a towel, only instead of a towel it's my brain, and not water but ideas. However, there are those moments as you are churning out bad ideas when a great one suddenly manifests before you. That's an exhilarating moment, a surprise, especially since before starting any given thumbnail, the idea that's about to manifest has probably never occurred to me. So, seeing it take shape as a scribble is the moment where I get the excitement any of you might get when you first see a new finished artwork, when you're confronted with that moment of surprise. That happens for me in the thumbnail phase. The rest of the process has pleasures of other kinds, but not like that moment.
But even after hitting one of these, it's important that I continue wringing the towel out for more and better ideas rather than stop at the first one that strikes me. That gets increasingly difficult the more concepts you turn out. So, there are some practical things I do to try to wring out new ideas, to keep inspiration levels high for as long as possible. I don't use them all for every project, but this series of posts will serve to outline a few, not necessarily in order of importance.
1.) Look at other art: over the years here I've had a
string of posts outlining
museums I've
hit up. As often as I'm able, I hit up museums and seek out artwork. Here in NYC, there are places I've gone to see art which aren't even museums but which have good artwork. I don't blog them all, but it's important that I expose myself to great artwork on a regular basis. It humbles me, helps me appreciate how far I've come (for instance, when I see something a painter in a museum did and think, "I can do that part."), and generally inspires me. Not doing so would be like being a musician who never listens to music. Absent a trip to a museum, reading through art books is a good secondary means to this end.
It's occasionally fun to see other artists, um, giving "homage" to some work of art that may be obscure to the public-at-large but is pretty well-known to those of us who dig in deep into various artists or historical eras of painting. I do try not to do this, to basically lift a composition from a historical work and re-dress it in outfits and things appropriate to my assignment. There may be times when this sort of completely intentional lifting of one iconic image is useful--see all the versions of American Gothic or Uncle Sam that have been painted over the years. But grabbing some more obscure work by Alma-Tadema, say, and repurposing it or large parts of it as an illustration, and thinking I'm passing it off as my own work--that I try to avoid.
However it is definitely the case that sometimes I may see certain problems solved, and I'll use their answer. A particular color gradation in a sky, perhaps a lighting scheme, the energy of a certain piece. In this way, I use other art occasionally as a springboard to head in another direction.