Keep track of what you need to do with a lightweight task list right inside of Gmail. Just click and type to add new tasks, convert emails into tasks, and (most satisfyingly) check them off as you're done. Once you turn on this Labs feature, look for the Tasks link to the left of your inbox under Contacts.
Send SMS text messages right from Gmail. You chat from your comfy computer and reach your friends on the go; they get your messages as texts and can peck out replies on their little keyboards.