http://todoist.com
Someone mentioned using this on another board and I decided to give it a shot. It's free, but the paid version adds so many awesome features.
It blows Outlook tasks out of the water. Everything is synced in Outlook, on my phone, the Chrome extension and on the web.
With the premium features you can set any email as a task. You can also add notes or attach files to any task.
Since most of us work on many projects, it even lets you organize you tasks by project.
It's free or $30/year for the premium ... but the premium is so worth it for the added features.