[pedalpete]

I am on the stand-up desk program and really like it. Though it isn't excercise from a cardio perspective, it can improve your posture (though like anything, you can still slouch at a stand-up desk).

I also sometimes stand on a balance board to make things a bit more interesting and engage core muscles while at my desk - though the second you touch your keyboard or mouse, you'd be amazed how much less you use your core for balance.