The two worked together on some 35 issues (though a few of the final ones featured other scripters, including Roy Thomas and Dennis O'Neil) - not including Amazing Spider-Man Annual #2, which featured an incredible team-up with the Doc and the webslinger.
This list is especially difficult because of the fact that so many of the best stories were continued - but we'll stick to individual issues here. So let's start the countdown at the bottom:
#10 - Strange Tales 115 - “The Origin of Dr. Strange”
One of the odd things about Doctor Strange's origin is that it took four issues to get around to it.
He first appeared in issue #110 of Strange Tales (sharing space with the Human Torch and Nick Fury over the years), then in #111 and #114. Apparently then it occurred to Stan and Steve to give us an origin story for the mysterious hero.
And in the 8-page gem they gave him a really odd origin.
The pre-Master of the Mystic Arts was a brilliant surgeon, but he was also conceited and heartless. A terrible car accident leaves his nerves damaged - he's no longer able to operate.
He spends all his money searching for a cure, and finally goes in search of the Ancient One, a mystic who might be able to offer a cure.
What Strange finds instead is a different world of powers and abilities he'd never dreamed of.
He accidentally sees Baron Mordo, a student of the Ancient One's, planning an attack on his master - but Mordo casts a spell the prevents Strange from warning the aged mystic.
Instead, Strange asks the Ancient One to teach him - and that begins his reformation, as he dedicates himself to standing against the forces of evil.
It's a lot to squeeze into a mere 8 pages, but Ditko manages to brew up some amazing atmospheric environments - and fantastic characters - in such a small space.
The story's not perfect - there are some big ol' holes in there to be covered (thankfully the film did a fine job of fixing the shortcomings of the original story) - but it's a powerful piece and a great start for the series.
The origin was a bit late, but well worth it.