Working at a high tech software company that sells call center software, I am constantly on the computer writing code, so anyways. One of my colleagues brought in an exercise ball, after sitting on a wobble chair for a while. I borrowed it the other day and sat on it throughout the whole workday. It is definitely a good way to keep your "core" stomach/abs muscles constantly in check/activated, because you constantly in balance and in good posture (or else you fall).
Wobble chairs vs Exercise ball, I'd vote for Exercise ball ;)