Remember the Milk is one of the most portable goal-setting services in its space. Users can create to-do lists with it, then access them in Gmail, via SMS, on mobile handsets, Skype, and popular IM clients. Because of this, you can access it from nearly anywhere, all without having to return to its Web site.
Remember the Milk also has an API that developers can use to integrate it into their apps.
There are two levels of service, one free and one Pro that runs $25 a year. Pro members get extra support, early access to new features, as well as access to the service on various mobile devices.