Here's one of the best potentially habitable extra-solar planets: Gliese 581 d.
Although Gliese 581 d orbits outside the theoretical habitable zone of its star, scientists surmise that conditions on the planet may be conducive to supporting life.[4][5] Scientists originally believed that Gliese 581 d would be too cold for liquid water to exist, and therefore could not support life in forms as existing on Earth. However, since Earth's temperature would be about -18°C[6] without any greenhouse gases, and due to a theorized greenhouse effect of Gliese 581 d, research now suggests that atmospheric conditions on the planet could create temperatures at which liquid water can exist, and therefore the planet may be capable of supporting life.[7][8][9]
