+1 about exercise. Also, remember there are different types of motivation. Intrinsic and Extrinsic. A monetary reward is extrinsic motivation, but nothing is as powerful as intrinsic motivation; the passion that comes from within. Maintaining it isn't easy, but exercise and socializing are useful for nurturing it in my experience. And yeah, as much as I preach about this stuff, I have periods of low motivation too. Sometimes you just need a break, just don't let that break fester.