The Pomodoro technique is phenomenal. I actually end up doing ~50 and 10 rather than ~25 and 5. The trick is, when the buzzer goes off, I hit save, mash make && make test and go grab a cigarette. Chat about the weather, video games, anything really with other folks (non-smokers are encouraged to take "smoke breaks" outside, get some much needed sunlight and just relax out of the cubicles). Come back in, look at compiler output or test results and there's a list of things to start working on. If it all ran fine, continue working.

Amazing how something so simple as "get up and away from your desk" does more than any "agile", "extreme" or "You're kicked from a plane, you must write a driver that interfaces the rip cord to the parachute release mechanism in order to deploy your chute" methodology.