Recently found: original 1941 concept sketches for Wonder Woman.
Here we have a piece of comic book history from early-1941 in the form of a letter from cartoonist Harry G. Peter, written to William Moulton Marston, in which he unveils some very early sketches of Marston’s new superheroine, Wonder Woman; Marston’s handwritten response to Peter can also be seen, penned in red below the original message. Wonder Woman’s subsequent debut came just months later - December - in All Star Comics #8 (cover). The rest is history. Transcript follows. (via Letters of Note: The birth of Wonder Woman)
ps: This sketch recently sold for $33,350. Yowza!