Jupiter

Equatorial Diameter: 71,400 km (11x R_earth)
Mass: 1.9x10²⁷ kg (320x M_earth)
Distance from Sun: 5.2 AU
Rotation period: 9.8 hours

Visited by:

Pioneer 10 & 11 (1973)
Voyager 1 & 2 (1979)
Galileo (now)

Jupiter has a very faint ring system, and an abundance (>60 and counting...) of moons, mostly small. The largest (Io, Europa, Ganymede, and Callisto) were discovered by Galileo, and can be seen through binoculars or a small telescope.