I'm not sure where I first heard about this, but it has drastically improved my productivity. It doesn't do much to get me started, but it keeps me from leaving my workflow once I'm already there. The short breaks keep me from getting too drained, but I'm always back on time and working again. I love being a slave to my timer.

I usually use http://tomatoi.st/ to keep track, but there are a bunch of other apps to help you out.