The Prison Workout

I have a gym membership at the local college, which is about 4 miles from my work. In the past (I've gotten pretty lazy lately) I'd run over at lunch, changing clothes as I drive, do a quick 20 minute workout, then drive back to work, changing clothes on the way, and throw down whatever food I had for lunch.
I'd have to rush the whole time. It wasn't very much fun, but I got my workout in.

I recently picked up a yoga mat at walmart. I've been doing some stretching and yoga over lunch.

Now, I'm expanding it to a yoga/stretch/workout.

If you google prison workout, you'll see there are tons of exercises you can do within the confines of your office.

I just got a pretty good overall workout, along with some stretching.

Pushups
Pullups (Lie under your desk and pull yourself up, keeping your torso straight.)
Squat thrusts
Lunges
Situps

Plus there are a ton of toning yoga poses.