Want to take your conditioning workouts up a notch? Throw in a bit of sandbag training. Love it.
The equipment is pretty simple. I personally use an Ultimate Sandbag (which I highly recommend - full review); and there are also several DIY options (the basic idea here).
In terms of space, the workouts don't require all that much - though it's great if it's available. As long as you have room to swing the bag in front of you and to press it overhead, you'll be fine.
There are many, many ways to train with a sandbag. Here are a few of my favourites :

There are also a number of superb sandbag exercises on the High Octane DVD. Highly recommended.
There's actually quite a bit of info (both online and offline) available on sandbag training methods, including :
Sandbag workouts are one of the few forms of training I perform daily. Once you try them, you'll quickly see why. Beautiful things.
Incidentally, if you’d like to discuss any of the stuff above, come and join us on the Straight to the Bar Community over on Google+. Absolutely free.