DailyDiary
DailyDiary is a no-frills, free, online journal and data-tracker. Diaries are created by asking and answering questions on a daily basis.
First, you set the things you want to track by asking questions, such as "how much do I weigh today?" or "how many minutes did I run today?" Daily Diary will send email reminders for each question and your responses will be tracked and displayed in graphs and charts.
DailyDiary is flexible--almost anything can be tracked--but the site is geared toward self-improvement.