SailorNeptune is of course inspired by the Neptune of Roman mythology. Since he was god of the sea, her powers are obviously water based:
Uranus was the Roman god of the sky, so SailorUranus has wind powers, but the attack 'World Shaking' always had me a little confused...
Although the Roman god Pluto was associated with death and the afterlife, SailorPluto's powers are more time-based. She is guardian of the Time Door and has the power to stop time, but her attack is still called, 'Dead Scream'
SailorSaturn is known as the soldier of destruction and silence. Saturn, in mythology, is a god of agriculture, but because he was the god that new when to plant and when to blight the fields, he became associated with death and the silence of winter. In the series, SailorSaturn explains that though she comes to destroy the world, SailorMoon is resposible for its rebirth.
All characters (c) Naoko Takeuchi
PS. The title of this post is based off the English translation of the theme song for SMS... I think DJ is probably the only one laughing