I always assumed Saucer Men was PD, since there seems to be bootleg poster, DVDs, etc.. all over ebay!
The studios didn't keep up the copyrights on posters, trailers and other such material, back then, so they fell into public domain. As for the movies, people will bootleg anything that isn't on DVD, yet, until somebody's lawyer sends them a C&D. There are some AIP titles that are PD, like LITTLE SHOP OF HORRORS, but most are owned by somebody.
Here's a list of links of movies you can watch online that I copied from my '50s sci-fi Yahoo group. Most are PD, but a few aren't and haven't been pulled, yet (the 2 hulu.com links are legit).
1984
Part 1 of 15 of the 1954 BBC production starring Peter Cushing.
www.youtube.com/watch?v=HPy0GGXYLRY Amazing Transparent Man - 1960
A crazed scientist invents an invisibility formula.
video.google.com/videoplay?docid=-6406228040079667584Assignment Outer Space - 1960
Rik Van Nutter. In the 21st century, a reporter is assigned to write a story aboard a space station.
video.google.com/videoplay?docid=8130113579409214470Atomic Submarine - 1959
Arthur Franz. Ships mysteriously disappear in the Arctic Sea, and a submarine is sent to investigate.
video.google.co.uk/videoplay?docid=2179625785784772906Attack of the Giant Leeches - 1959
Yvette Vickers. After a local man sees a giant creature, people start disappearing.
video.google.com/videoplay?docid=-6910485032449825448Attack of the Puppet People - 1958
John Agar. Lonely, deranged puppet-master designs a machine that shrinks people.
www.hulu.com/attack-of-the-puppet-people Battle of the Worlds - 1961
Claude Rains. A stray planet on a collision course with Earth instead takes orbit around our planet.
video.google.com/videoplay?docid=5274453589446386855Beast of Yucca Flats - 1961
Tor Johnson. A defecting Russian scientist is transformed by an atomic test into a hulking monster.
video.google.com/videoplay?docid=4913900592490278110Brain That Wouldn't Die - 1962
Jason Evers. After a car crash, a man keeps his wife's head alive in his laboratory.
video.google.com/videoplay?docid=6660611491774828467Day the Sky Exploded - 1958
Paul Hubschmid. Scientists discover that a group of meteors are hurtling on a collison course with Earth.
video.google.com/videoplay?docid=7019572511814987166First Spaceship on Venus - 1962
Yoko Tani. A mysterious magnetic spool found during a construction project is discovered to have originated from Venus.
video.google.com/videoplay?docid=6479082962502567246Giant Gila Monster - 1959
Don Sullivan. A giant lizard terrorizes a rural Texas community.
video.google.com/videoplay?docid=2698609172520943638 Here Comes Tobor
Unsold TV pilot from the late '50s.
tv4u.com/show-video.asp?cid=20&sid=756&vid=2269&t=Here%20Comes%20Tobor&cat=Hi%20TopsInvasion of the Saucer-Men - 1957
Frank Gorshin. A teenage couple making out in the woods accidentally runs over an alien creature with their car.
video.google.co.uk/videoplay?docid=-3632366363646782409Journey to the Seventh Planet - 1961
John Agar. Expedition to the planet Uranus discovers a bizarre world right out of their own heads.
video.google.co.uk/videoplay?docid=-4947319747872402517Killers From Space - 1954
Peter Graves. A scientist, killed in a plane crash, is revived by aliens so he can help them conquer the world.
video.google.com/videoplay?docid=7140333716173454857La Jetée - 1962
Jean Négroni. This classic French short (27m) inspired the movie "12 Monkeys". English narration.
video.google.com/videoplay?docid=4536409644066983943 Lost Missile - 1958
Robert Loggia. A strange missile from outer space circles the Earth, destroying everything in its path.
www.classiccinemaonline.com/cinema/sci-fi/thelostmissile.html Phantom From Space - 1953
Ted Cooper. Invisible alien crash-lands near L.A. and wreaks havoc on city.
video.google.com/videoplay?docid=-2482536613503089996Phantom Planet - 1961
Francis X. Bushman. Mysterious unknown planet of miniature people, giant monsters and beautiful women.
video.google.com/videoplay?docid=6928708777839415241 Plan 9 From Outer Space - 1959
Dir. by Ed Wood. Aliens reanimate corpses in a plot to take over the world.
video.google.com/videoplay?docid=-7038656109656489183Project Moonbase - 1953
Donna Martel. United States is considering building bases on the Moon.
video.google.com/videoplay?docid=-7798957258263736104Radar Men from the Moon - Chapter 1
George Wallace as Commando Cody. Strategic targets on Earth are being destroyed by an unknown weapon. Chapters 2-12 also available for viewing.
video.google.com/videoplay?docid=-6026193486040846592 Strange World of Planet X - 1957
Forrest Tucker. Man and alien unite to combat the most insidious peril the universe has ever known! aka The Cosmic Monster
video.google.co.uk/videoplay?docid=-2882043160690211207Teenagers From Outer Space - 1959
David Love. Maritans invade earth to grow their "Gargon" herd.
video.google.com/videoplay?docid=7514991260001615807 Unknown World - 1951
Victor Killian. A group of scientists build a drilling vehicle and journey inside the Earth.
video.google.com/videoplay?docid=-1289054165158099038Voyage to the Bottom of the Sea - 1961
Walter Pidgeon. Admiral Nelson takes a brand new atomic submarine through its paces, when the Van Allen radiation belt catches fire.
www.hulu.com/show/483/voyage-to-the-bottom-of-the-seaWarning from Space - 1956
Toyomi Karita. UFO's, that look like giant starfish, are seen around Tokyo.
video.google.com/videoplay?docid=8681177696242678241Wasp Woman - 1960
Susan Cabot. A cosmetics queen develops a youth formula from jelly taken from queen bees.
video.google.com/videoplay?docid=-2561413428612719802 
