Gmail Labs finally got around to adding an integrated task list in Gmail. The task window popups like a chat window while you’re in gmail allowing you to to keep it open while you surf or browse through other email.
To enable Tasks, go to Settings, click the Labs tab (or just click here if you’re signed in). Select “Enable” next to “Tasks” and then click “Save Changes” at the bottom. Then, after Gmail refreshes, on the left under the “Contacts” link, you’ll see a “Tasks” link. Just click it to get started.
You can also easily convert emails into tasks: select one or more messages and go to More Actions > Add to Tasks. (Or turn on keyboard shortcuts and use <shift> + t.)