I prefer http://www.joesgoals.com/ - it allows you to set up multiple chains and manage them from a single page.

Joe's Goals is great because you can do negative goals too ("checked email off-schedule", "browsed HN during work hours", etc). It's compelling to see if you can beat your numeric value from the previous day.

Thanks. Signed up and giving it a shot. Positive goals: push-ups, reading, cooking. Negative goals: playing a game of Freecell. ;)