I used to use Remember the Milk (RTM) quite a bit last year for task managing, but lost interest a bit this year as it was too separate from other things. The ability to send tasks via Twitter was certainly something that rekindled my interest a bit, but now I am fully back on board with this fantastic Firefox extension Remember the milk for Gmail which lets you manage your tasks right within your Gmail account. You can add new tasks, complete, postpone, and edit tasks. But, even better, it also allows you to connect tasks to your Emails, Contacts or Google Calendar events.

RTM