"Unusual Tales", a series presenting Steve Ditko's comics from 1957 to 1959 that are in the public domain.
As previously discussed, Ditko drew 20 covers for Charlton during his first stint there, published in 1954 and 1955. Ditko covers resumed in 1957, and he drew some great covers during the rest of the 1950s, mostly for Charlton (with three Marvel covers in early 1959 and one other one seen below). A dozen of them were previously posted here. Another dozen are printed in the recent Ditko/Snyder co-publication THE COVER SERIES. Everything else appears below.
My comments on the covers below, click on the thumbnails for larger scans.
Some links to check out:
New material and classic reprints, including THE COVER SERIES
New issue out now
Lots of public domain Ditko from various publishers available
Scans in this series generally adapted to my personal tastes from those copies
DO YOU BELIEVE IN NIGHTMARES #1 
The only non-Charlton cover in this set to start us off, I discussed what little I know about this oddity in Ditko's late 1950s career in this post about one of the five Ditko stories. Very striking cover, unrelated to any of those interior stories, Ditko horses are always interesting to see, as are Ditko birds, so a winged horse by Ditko is doubly interesting.
CHEYENNE KID #10 
And another oddity, I think that this is the only western cover that Ditko drew, other than a few ink jobs over Kirby for Marvel. No Ditko interiors this issue, so we're left with this single rendition of Ditko's version of Custer's Last Stand. Not that the actual interior story on the theme is a let-down, being drawn by Al Williamson and Angelo Torres.
TALES OF THE MYSTERIOUS TRAVELER #6 
And something more typical, a Traveler cover with a large imposing figure of our host, along with teasers for three of the Ditko stories inside, "The Old Fool", "Tomorrow's Punishment" and "When Old Doc Died"
THIS MAGAZINE IS HAUNTED #14 
And the Traveler's less subtle companion Dr. Haunt teases another trio of Ditko tales. The blurb for "The Green Man" is kind of large and visually boring, unfortunately, but I do like the tattered posters on the ground for "The Second Self" and "From Out Of The Depths".
UNUSUAL TALES #10 
A great cover, completely unrelated to any of the stories in the issue, which only get text blurbs across the bottom. Intriguing looking figure, and I like the unusual shading method used to get the foggy look.
MYSTERIES OF UNEXPLORED WORLDS #10 
Also unrelated to any of the interior contents, I like the look of the water, and the shadowy alien figure in the ship, and that large tree in the foreground drawn in negative space.
MYSTERIES OF UNEXPLORED WORLDS #11 
This is one of those unusual pieces signed "J. Kodti" (sometimes "J. Kotdi"). Impressive cover, I always like the weird alien fish. No story to go with this cover, unfortunately.
STRANGE SUSPENSE STORIES #40 
Unrelated to the interiors, not really one of my favourites, though there are some interesting inking techniques.
TALES OF THE MYSTERIOUS TRAVELER #11 
I suppose a case could be made that this cover goes with the story "Inside The Crystal Globe", although the design of the villain of the piece is quite different. Still a very nice cover, whenever I see it I imagine it as a Doctor Strange cover, with Doc in place of the Traveler and a title like "The Menace Of The Other Ancient One".
UNUSUAL TALES #15 
For a few months in 1959 Charlton had their "Win 8000 Prizes" promotion, which unfortunately they chose to plug on the cover with that giant prize ribbon on every book. A trio of Ditko covers got that treatment, but they're still great covers, especially this one. Unrelated to any interiors, and interestingly with a visual theme Ditko would return to a few times in stories he wrote in the 1980s.
OUT OF THIS WORLD #12 
Unrelated to the interiors, though both the diving suit and the drilling machine resemble elements from stories in other books.
OUTER SPACE #21 
Again unrelated to the interiors, proud American astronauts captured by aliens. Very nice, though I question the design of a space suit with bare hands...
And four more...
In the late 1950s it became pretty common for Charlton not to run original artwork on the covers, but instead use interior artwork, often with modifications, for the cover. These are the first few examples of such covers by Ditko, there would be a lot more in the 1960s.
STRANGE SUSPENSE STORIES #37 
An image taken from the opening page of "The Dancing Cat", with some heaving reworking on the cat figure.
TALES OF THE MYSTERIOUS TRAVELER #10 
The Traveler headshot comes from "Little Boy Blue", with some modifications, and a panel from that story and from "The Statues That Came To Life" complete the image.
SPACE ADVENTURES #31 
A combination of two panels from "The Enchanted Planet".
OUT OF THIS WORLD #16 
A combination of several panels from "The Little Things".
Some excellent covers. I'd probably go with UNUSUAL TALES #15 as my favourite of those, but there are several strong contenders.