Google have released yet another addition to the Gmail service that they have, a to-do list. It is called by them ‘Tasks’ and can be accessed by clicking on the beaker looking icon next to the Settings button.
You can add to-dos, change the order, tick them onced you have completed them and can add a due date to each to-do. Sadly, you can not yet send your to-do to others through an email but that might come later.
Here is a screenshot of it: