How can I have a decent workout without leaving the house?

I have an exercise bike and it works well since it is relatively stable and does not make much noise. You could also try a self-propelled treadmill that is foldable that works well in a house. If you have the room try getting a cross country machine, stair stepper, or motorized treadmill. Also, rowing machines are really good since they don't take up that much room.