Check out http://www.shovelglove.com/
Buy a 5-10lb sledgehammer at the local hardware store, wrap the hammer portion in something absorbent, like a towel or somesuch. Can do a variety of exercises, cardio, strength training, flexibility, website should give you the basic lowdown, there are also videos on youtube. The awesome thing about this is:
1) Don't need to go to a gym, or outside, can be done in your own bedroom if it's not too crowded
2) All sorts of exercises you can do, like pretending to shovel snow, or putting posts in the ground, or chopping down a tree with an axe, lifting an overhead door, carrying heavy groceries, and so on. Can make it fun, not too monotonous.
3) Very easy to, in the middle of the day, walk over to the shovelglove, pick it up, do 2 minutes of a random routine, then maybe again later in the day. Nifty for people with short attention spans.