If you really want a challenge, here's what I used to do for martial arts conditioning:
LOTS of headstand puch-ups-if you cant do a headstand, practice against a wall for a while OR do bunches of inclined push-ups w/feet ontop of couch, crates, bench, chair, etc.
Sandbag training-basically, use any sort of heavy bag (I used an 80 lb bag of wawter softner salt for weeks) and be imaginative. Go up and down stairs, do squats, leg presses, lunges, shoulder presses, etc.
If you like pain-do martial arts/boxing interval training....
such as, but not limited to...
run with sand bag,
stop, do sandbag squats,
sprint with sand bag,
stop, do push-ups of any kind 'till failure,
run with sand bag,
stop, drop sandbag, do pull/chin-ups 'till failure
jog to start and back, pick up sand bag and repeat until you puke/pass out.
