Titan is larger than Mercury and the Moon (though second to Jupiter's Ganymede). Titan has no magnetic field and sometimes orbits outside Saturn's magnetosphere. In the near infrared the haze becomes more transparent, and HST's pictures suggest that a huge bright "continent" exists on the hemisphere of Titan that faces forward in its orbit. These Hubble results don't prove that liquid "seas" exist, however, only that Titan has large bright and dark regions on its surface.
Saturn's remaining moons
The remaining moons show heavy cratering, though Enceladus appears to show evidence of more recent geological activity, having a relatively crater-free region on its surface. All of the moons, including Titan, are tidally locked to Saturn. See ground based image here.
Interactions between Rings and Moons
There are complex tidal resonances between some of Saturn's moons and the ring system: some of the moons, the so-called "shepherding satellites" (i.e. Atlas, Prometheus and Pandora) are clearly important in keeping the rings in place. Shepherd satellites or moons move just inside or outside of a ring system, and confine the narrow rings through their gravitational effect. Moons can also clear out sections of the rings: Mimas seems to be responsible for the paucity of material in the Cassini division; Pan is located inside yet another gap (Encke Division). The whole system is very complex and as yet poorly understood. A diagram of the ring and moon system is shown HERE.