There is a spray for the upholstery that will help. I don't remember the name, but it should be available at any parts/accessory store.

and I found that I could avoid getting zapped by touching the key to the door lock.

it is a fabric spray, like all products you might want to try it on a hidden spot first.

Are the seats cloth or leather? Cloth tends to be susceptible to this if you slide your butt across the seat when you get out.

You can try not to do so, or there are anti-static sprays you can place on the cloth. I am not personally familiar with them or how it might be different with leather interior.

Here's a free solution to the problem.

Hold on to your car's door until your foot touches the ground. Once you're on the ground, then close the door. It may seem like you're pirouetting around a bit, but it'll solve your static problems. :)