I work at a desk, study at a desk, update my blog at a desk. All this time on my backside means that my general 'accidental' activity levels are pretty lousy... until I made this bad boy:
Behold! The cup of inactivity death!
I bought a couple of cheap-as-chips packets of plastic knives and used a fine tipped Sharpie to write different exercises on each. There are about 40 in total, each with an exercise that lasts roughly a minute. Every half an hour, I pull out a knife or two and get moving!
All of the exercises I used are great for small spaces, and if you're feeling self-conscious about doing burpees in your busy office (haha!), try things like calf raises, stretches (like quad stretches at your desk), go for a 5-minute walk, get up and down from your seat 10 times (no using your hands!) or do a couple of laps around the office. Make it work to suit you!
You can also use popsicle sticks, but pulling out a knife makes you feel more bad-ass.