This list is in no particular order...
1. John Wayne Gacy AKA The Killer Clown
John Wayne Gacy was active from 1972-1978 in Chicago, Illinois. He is known to have sexually abused and murdered 33 boys and young men. Often he would entice his victims back to his home (which has since been burned to the ground) by force or with the promise of money. There he would strangle his victims and bury them in the crawl space of his home. In 1980, he was convicted and sentenced to death. After 14 years on death row, he was lethally injected in 1994.
A good documentary: "Serial Killers- John Wayne Gacy (Killer Clown)"
2. Aileen Wuornos
Aileen, one of, if not the most famous women serial killers, was active between 1989 and 1990 in Florida. She murdered several men by shooting them, claiming they had been attempting to rape her and that each murder was done in self defense. During her years in jail, Aileen did many interviews up to her death. In 2002, she was lethally injected on October 9th.
A good documentary: "Aileen: Life and Death of a Serial Killer"
You can watch it on Netflix.
3. The Zodiac Killer
One of the most famous unidentified serial killers out there, along with Jack the Ripper, of course. He was active from 1968 to 1969 in northern California. In total there were five murders, beginning with a couple parked at lovers lane. Betty Lou Jensen was shot 15 times and David Faraday was shot in the head. The Zodiac Killer makes this list, not because of his murders, but because of his need to rub them in the face of the police working on the crime. After his second murder on July 4, 1969 he called the police an hour after the crime was done stating "I want to report a double murder. If you go one mile east on Columbus Parkway to the public park, you will find kids in a brown car. They were shot with a 9mm Luger. I also killed those kids last year. Goodbye." He also wrote the famous "zodiac letters" that still confuse people to this day and have yet to properly be decoded.
A good documentary: "This is the Zodiac Speaking"
4. Gary Ridgeway AKA The Green River Killer
Active from the years 1980-1990 in Washington. Gary admitted to killing 49 women, his victims mainly being young runaways as well as prostitutes. He strangled his victims before disposing of the bodies. The first five victims were found in the Green River, hence his nickname, however often they were simply dumped in overgrown areas. Often he would return to the bodies after in order to have sexual intercourse with them. In 2001, he was arrested after four cases were linked to him through DNA evidence. As part of a plea bargain he agreed to disclose the location of the other bodies. As a result, he was spared the death penalty and instead given life imprisonment without parole.
A good documentary: "Gary Ridgeway: The Green River Killer" (2003)
5. H.H. Holmes
Dr. Henry Howard Holmes, better known as H.H. Holmes was the first serial killer in America. His killing spree lasted from 1891 to 1894 in what came to be known as his "Murder Castle" in Chicago, Illinois. This murder castle had soundproof rooms, secret passages, a never-ending maze of hallways and staircases, and doors that lead to nowhere. During its construction the crews were constantly fired and new ones were hired, no one knew what the entire plan of the hotel was except Holmes himself. While Holmes claimed to have killed 200+ people in his confession, he was only convicted of the murders of Pitezel, his two daughters, as well as his son. In 1896, Holmes was hanged for his crimes.
A good documentary: "H.H. Holmes: America’s First Serial Killer" (2004)
You can watch it on Amazon.