Whether it's hitting the gym, calling your mom, or feeding the child locked in your basement, sometimes no amount of string tied around your fingers can remind you of your responsibilities. Try HassleMe.
British site HassleMe's free service is as self-explanatory as it is effectively annoying. Enter in the message you want to be reminded with, the frequency of hassling you desire, and the email address you want to be bugged at. Once you confirm that you really do want to be harangued by a 'bot, you'll get the scheduled prompts you need to start living like a functional adult. Some examples (with frequencies)
Call your grandma (twice a year)
Call your ex-girlfriend to breathe heavily into the phone (every couple days)
Floss (4x per week)
Build up immunity to iocane powder with increasing, semi-weekly doses (semi-weekly)
Eat a fruit or vegetable (once a month)
Take a photograph; remember Sammy Jankis (daily)
In the near-future, HM will be adding IM hassling as well as increasing interval specificity down to the hour -- so you can bracket your work day with reminders to start reducing the number of inane automated emails you're receiving.