When I go to the gym, I tend to focus on one cardio machine a day. Whether I'm using the elliptical, the stepper, the stationary bike, or the treadmill, I usually get on it and stay on it. Occasionally, I play around with different machines using Gunnar Peterson's 4-5-6-6-5-4: Cardio Plan. It definitely breaks up the routine.
So, what about you?