A training regime that my buddy has me started on that lasts about 25min roughly and works on pushups, sit-ups and jogging all together...he calls it MEL!??!
anyways works like this:
if you take the top half of a football pitch- start from the halfway line and jog up and around the top and down to the other half way line- during this you stop at designated points; these points being the first corner you come to, the second corner you come to and the other half line and back through all points again and again....at each point you do the physical excercise, ie push ups and sit ups. however at each point you reach, you increase the number of each reps by one so example of this:
run from halfway line to the first corner- do one push-up and one sit-up and jog to next corner then do two push-ups and two sit-ups etc etc
now the idea is that you build up to 20 of each, and then you count back down so 1 too 20, then 20 too 1.
i started this excercising a short while ago and got up to lvl 10 and i was done for the day! so i recommend you start easy and build your way up gradually....
but this way you do a lot of workout in one go.