I park 3/4 mile from my work so I get a 1.5 mile walk in every day. I also leave work for lunch most days, so I get another 1.5 mile round trip on those days. I base the distance on the weather, so on sweltering hot days or frigid cold days I park closer.
It's a good distance for me, but not long enough to sweat too much. At the end of the day I have gotten some great exercise in, but never get the "I don't feel like exercising today" feeling anymore.
Used Google Maps to find some good places to park near your work.. some different spots to change it up a bit.
I think this "exercise" works for me because I am tricking myself into believing it isn't exercise at all. It's just how I get to work now. My mind is so gullible. Whatever works, right?