When I get that feeling, I know it's about time for a week or so of vacation. I have to break the routine up as much as possible, and stay away from the computer, cell phone, tv, etc.. For me, getting out of town and going camping, kayaking, or skiing for a few days usually does the trick. Even if you're tight on cash and can't get out of town, just intentionally detoxing from technology can be incredible for recharging your batteries. You don't realize how exhausting it is being tied to your cell phone or laptop until you get away from it for a few days.
Best of luck getting out of the rut.