Ceres \((1801)=\) Cerium (1803)

Pallas \((1802)=\) Palladium (1803)

Neptune \((1846)=\) Neptunium (1940)

Pluto \((1930)=\) Plutonium (1940)

All were named after large solar system bodies, which, at the time the elements were named, the corresponding celestial bodies were considered to be planets. After discovering many more asteroids, Ceres and Pallas were demoted to asteroids in the asteroid belt. Pluto was also demoted, much more recently, to a dwarf planet, which also resulted in Ceres being 'promoted' to dwarf planet status! Pallas is too small to be considered a dwarf planet, so it is still considered an asteroid. Obviously Uranus and Neptune are considered planets, being the \(4^{th}\) and \(5^{th}\) largest bodies in the solar system. Mercury is the name for a planet and an element, but as Daniel Spector mentioned in his answer, they are both named after a god, rather than the element being specifically named after the planet.