Honest to goodness science fact here regarding tidally-locked moons in orbit around gas giants:
Several moons in our own solar system are strong candidates for hosting water-based life, the most promising being Europa, which orbits Jupiter.
On its surface, Europa is a frozen ice ball that is uninhabitable because it lacks an atmosphere (also, it is irradiated to hell by Jupiter). This moon is too far from the Sun to receive much solar warmth, and so the surface ice is permanent.
However, there are no craters on that ice surface, telling us it is continuously renewed. And analyses of its mass only make sense if there is a deep ocean of liquid water beneath the ice.
As it turns out, tidal locking exerts other forces on Europa (and other similar worlds). On Earth, tides are mostly observed in the rise and fall of the oceans, all caused by the orbit of the Moon; we can see our liquid oceans rising and falling several times a day, but the land seems immobile. With the gas giant moons, however, the planet's gravity exerts a pull on the rocky cores, sort of kneading them like bread dough. These tidal stresses sustain tectonic activity where it otherwise shouldn't exist. (By contrast, the reason why Mars is a poor candidate for life is because its atmosphere mostly blew away, and its molten iron core cooled and solidified.)
So, the hypothesis is that Europa possesses more water than Earth, and that it is kept in a liquid state by a substantial amount of hydrothermic activity created by tidal stresses. These vents would be comparable to the Mid-Atlantic Ridge, where ecosystems of microbes and multicellular organisms thrive on the mineral-rich heated water, completely independent of sunlight. If life exists on Europa, it would be based on these kinds of microbes. Whether or not multicellular life could exist in that environment would depend on how oxygenated the ocean is; Jupiter's radiation could be creating oxygen on the moon's surface, which may then be falling into the ocean below through fissures in the ice.
This isn't idle speculation found on some sketchy blog; this is NASA's theory, and they have a Europa-bound probe scheduled to launch in 2022. There are other moons in orbit around Jupiter, Saturn, and Neptune where the potential for life can't be ruled out; the moons of Uranus are too little known.