Here are some study results which are right up Lifehacker's street. According to researchers at Stanford Uni, an automated computer message reminding people to get out and exercise is almost as effective as having a human counseller do the same job.
The study found that people called by the computer with an exercise reminder averaged 157 minutes of exercise per week, compared to 118 minutes for the people who didn't receive a reminder.
We've offered up a range of reminder apps in the past ranging from setting up email reminders for recurring activitites with HassleMe, text message alerts with iCal, or you can do what I do and set up SMS alerts through Google Calendar. Got a system for automated exercise reminders? Please share in comments.