I try to exercise outside in an enjoyable place as much as possible. It is really convenient to have an elliptical at home, but that doesn't "feed" my soul the same way as taking a quick-paced walk in the woods or doing some yoga in my yard. Good for mind and body! :-)
I add intensity to walking outside by wearing 1 lb. wrist weights and really swinging my arms. Sometimes I'll do curls or other lifts to the rhythm of my walking. I'm really a really good book about walking -- "Chi Walking" by Danny Dreyer.