i've had good success following DVD workout programs. i find following along to the workouts to be a better motivator than jogging a bit and lifting some weights, not that there is anything wrong with that-it is whatever works.
but re: the op, when it's come time for me to start another p90x cycle and i'm a bit out of it or not feeling like it, i start off with the beachbody 10 minute trainer, just 1 10 minute session a day for a couple days then i am easily adding 10 minute sessions until i am at 40 minutes which is usually enough to get my motivation and such going enough to begin a p90x cycle.
http://www.beachbody.com/product/fit...er.do?t=tmt1b2