Done This

The fun, easy way to get stuff done.
Every day they email you to ask, “What’d you get done today?”

Just reply to the email to make an entry.
Inch by inch, anything’s a cinch.
They keep a calendar for you of what you got done.

Look to your streak from yesterday to motivate you today.
I've been doing this for the past month or so and found it to be fun and very easy!
Forget to enter, no problem, as long as you saved the email, just hit reply, add your list, and send it off. Use it for whatever you want! (Weight loss, calories consumed, miles walked or ran, etc. -the possibilites are endless!)

Goals you've reached each day, items off your checklist, an easy way to journal, you'll see you'll want to do just something to get that checkmark in the calendar box!
To look back at your accomplishments just click on a checked box and see your list from that day. Come on, give it a try! I think you'll find it very motivating!

http://idonethis.com/

Update:
My friend Diane wanted to know about the ability to print out what's been accomplished on Done This and wrote them an email and got this reply:

"Can I print my calendar entries at the end of the month? If so, how would I do this?"

Diane, thanks for your email!

To print out your calendar entries in aggregate, just go to your settings. Click "Export", and you'll get a file that has all of your entries. If you open that file up in Google Spreadsheets or Excel, you'll be able to view all of your entries and print them out.
Please let me know if you have any troubles with this!

(Thanks Diane for taking the time to find this out, You Rock!)