Nimbus - "Nimbus" means "cloud." Nimbus was also a god in Greek Mythology.
Norris, Mrs. - A character in one of J.K. Rowling's favorite author's (Jane Austen) books.
Parvati - Parvati is a Hindu Goddess married to Hindu God Siva the Destroyer. She gave birth to a baby boy named Ganesh, who Siva beheaded, but replaced the old head with an elephant head after Parvati reamed him out. Sister of the Goddess of the Ganges, Padma "Patel" is a common Indian last-name.
Peeves - "Peeve" means "little devil" or something that gets on your nerves (like a pet peeve).
Petunia - Petunia, the flower, is always thought of among florists as meaning resentment or anger.
Pomfrey - Comfrey is the name of a very good medicinal herb still used today.
Remus - Brother of Romulus (founder of Rome). They were raised by a female wolf. He was killed by Romulus.
Ronald - Ronald's name comes from a legend of a great emperor from the 6th dynasty of a certain family. This emperor, Running Weasel, never lost a game of chess. But sadly, the guards outside his home accidentally let loose a rat dyed yellow. The rat started a fire, which Running Weasel died in.

6th dynasty? Ronald was the 6th born in his family. He own a rat, which he tried to turn yellow in the first book and accidentally set loose in the 3rd book. Wormtail happened to be a coward, another translation of the word yellow. Ronald has yet to lose a game of chess and has actually turned out to be a nice strategist. Who else owns a rat?
Ronan - An Irish saint
Rubeus - Meaning Rubees. (See 'Hagrid')
Severus - Sever means "to cut-off". Severe also means cruel, strict. In ancient history, Lucius Septimius Severus restored stability to the Roman empire after the tumultuous reign of the emperor Commodus (See Albus) and the civil wars that erupted in the wake of Commodus' murder (if you watched "Gladiator" then you should know this).
Sibyll - Sibyll comes from the Sibyls, who were famous prophesy in ancient mythology.
Sirius - Named after Sirius Star, or Dog Star. Seen during summer "dog" days.
Skeeter, Rita - "Skeeter" is short for "mosquito." As most people can attest, mosquitoes are among the most annoying life forms on this planet.
Snape - A town in England, also based after a person JKR knew.
Tom Marvolo Riddle - If you rearrange the letters it spells: "I am Lord Voldemort."
Viktor - Victor actually means Victor in Latin. It's short and dull, and doesn't have any significance to anything.. Just like Viktor Krum is thickheaded and not much brains?
Voldemort, Lord - There was a dark wizard in mid-evil times named Voldermortist. In another language, Voldermortist means "Lord of Evil" or "Dark Lord". Legend has it that Voldermortist once tried to destroy Merlin before the time of King Arthur (Mr. Weasley?), by bewitching good people, and simply bribing those who already were evil. Legend has it that Merlin destroyed Voldermortist by using a simple paralyzing charm (full body bind?), fed him to the many-headed-beast (Fluffy?) of the lake, the Lady of the Lake's pet (Giant Squid?), freed the bewitched people, and destroyed the evil men. That was maybe twelve, thirteen years before Arthur (how long it was from Voldemort's destruction until Harry started Hogwarts). In French means "thief of death" (meaning escaping death).