I do the Tabata protocol on an eliptical. 5 minutes warm up then alternate 20 seconds all out max effort with 10 seconds of recovery for 8 rounds in 4 minutes. I ramp up the resistance during the max effort phase also. I call it 4 minutes of hell. Then I'll usually do about 15 minutes in the fat burning heart rate zone after. Works great for me and its quick. But it is hard as hell.

Try a quick little 15 minute stationary bike HIIT.

http://www.fitocracy.com/knowledge/dr-layne-nortons-best-damn-cardio-hum...

If treadmill is out of the question then your pretty limited to a concept rower, stair master,

Rowing machine
1) 3 min 50% row for warmup
2) 1 min max intensity, 1 min moderate
3) 2 min max, 2 min moderate
4) 1 min max, 90 seconds moderate
5) 90 seconds max, 1 min moderate

Do this in completion 3 times through

Treadmill: 10 incline, 15 mph (sprint 15, rest 30) 20 reps

Stairmaster
2 minute warmup at level 5
1 minute level 10
30 seconds level 7
1 minute level 11
30 seconds level 8
1 minute level 13
30 seconds level 9
1 minute level 14
30 seconds level 10
30 seconds level 15
1 minute level 10
30 seconds level 14
1 minute level 9
30 seconds level 13
1 minute level 8
30 seconds level 12
1 minute level 7
30 seconds level 11
3 minute cooldown level 5

I do HIIT on the stair master 3 days a week. I choose the Interval program for 20mins and usually gets me 1 min intervals or high intensity and 1 min or low/rest. I've done this for years and at times have been down to 6% bf at 210lbs.

I used to do HIIT on the treadmill but it was to much for my knees and shins to take. I would lightly jog for about 5 min to get warmed up and then go into my HIIT intervals. I would sprint as fast as possible for 1 minute and then slowly walk for 1 min and repeat. I would do this for 10 intervals and then lightly jog for 5 min or so to cool down. When you first start out you may not be able to do 10 intervals but gradually work yourself up to 10.

Now I just recently started doing HIIT on the bike machine. I have found I get just as good of a workout and my joints are thanking me too. I do HIIT training at least twice a week. These are the two days when I am not lifting. I wouldn't recommed doing HIIT and a workout on the same day. I think the stair stepper would also be a good HIIT routine. I'll maybe try that next when I get bored on the bike.