How do you do your cardio?

Katie P asks, so I shall answer! Actually, I don't have one answer... I have many, so I'll share a few. Feel free to adjust the levels/goals for your own fitness. I usually mix cardio and weights all into one session, so some of these are quite short.

Option 1: 6 minutes of intervals
Cross trainer (although would work on bike or tready)
5 minute warm up - moderate pace
1 minute hard (level 12, fast as you can go)
50 seconds easy (level 10, walking pace)
50 seconds hard
40 seconds easy
40 seconds hard
30 seconds easy
30 seconds hard
20 seconds easy
20 seconds hard
10 seconds easy (don't change the level)
10 seconds hard

Option 2: Treadmill sprints
5 minute warm up jog
90 seconds fast (HR 85-100%)
30 seconds off (stand on side of t'mill but keep it running)
repeat 4 times
15 minute weight circuit
repeat sprints

Option 3: Mixed cardio (only works well when the gym is quiet, or if there are 3 of you to keep one of each machine)
5 min warm up on whatever you choose
3 min bike (level 11, RPM above 35)
3 min cross trainer (level 12, goal: 48 calories)
3 min treadmill (10km/hr)
10 pushups
2 min bike (level 11, RPM above 35)
2 min cross trainer (level 12, goal: 32 calories)
2 min treadmill (10.5km/hr)
10 pushups
1 min bike (level 11, RPM above 35)
1 min cross trainer (level 12, goal: 16 calories)
1 min treadmill (11km/hr)
10 pushups

Option 4: Circuit with PT (my fav)
5 min warm up cross trainer
2 min bike (level 11, RPM above 35)
2 min boxing
2 min skipping
2 min crunches
2 min cross trainer
repeat x 3 times