What Emile said, although I do have to make sure I don't cheat! (Also, the M&Ms are in a desk drawer where I can't see them) Before I tried this, every time I goofed off during a pomodoro, the mild buzz of surfing the internet served as a reward. Now, I tell myself, "don't goof off, or no M&M for you!"

There's a second reward as well, which may not apply to everyone equally. I work full-time, basically in legal research. I used to spread 10 pomodoros out over the day (okay, 8). Now I do 10 as fast as possible, and then switch to personal research. This makes the day much more pleasurable. The M&Ms reinforce this faster-moving, more engaging schedule.