Star Spangled Comics # 7, from 1942. Cover by Kirby with Joe Simon inks. The first appearance of the Simon/Kirby Newsboy Legion. Not as well known as something like Kirby's X-Men, but a great example of Jack's ability to knock out teams of heroes seemingly effortlessly.
I would've bought this book not only for the great Kirby-Simon artwork, but also to find out who Robotman and the Tarantula were.
Terrific splash page. With one image, Jack has introduced you to the basic premise of the series -- a police officer who is secretly the Guardian, and a group of misfit kids off on an adventure.
There are plenty of great examples of noteworthy Kirby art throughout, but I pulled pg. 9 as one example to show how Jack loved to have his characters bursting out of the panels.
Notice in this close-up, there are characters from the other panels crossing over the square border of the frame. This creates a sense of chaos where the characters are so packed together within the various frames, they can't seem to help but stumble out of them and overlap. This style gives the work a 3-dimensional look, and probably reflects Jack's experiences growing up in the crowded streets of New York.