In school some kids used to do some isometrics, especially abs, while in the desk and some pushups at breaks. Some kids were more motivated to do it than others. I am looking forward to looking at the topic, maybe there is something for windshield time.
Not sure if you have stairs or not in your building. I work on the 5th floor and whenever I need a break or go to the restroom I make myself walk up and down twice. Nothing special but I like it.
The local fitness community where I am posted this workout a while back on their twitter page. It is pretty solid for arms core and legs. You can do it in a cubical and its quick. I try to do something every hour through the day. Even a set of lat dips on the chair between meetings helps.