My dad gave me a copy of Up Front and since then I've been a big fan of Mauldin's wartime work - it's one of my favorite books about the war. In his later memoirs, The Brass Ring, he mentions most of his books and booklets that were published, so I've tried to get all of them. However, I'm certainly not an expert and haven't gone back to verify the order.
1941 Star Spangled Banter The first of several with the same title, done at the time of the Louisiana Maneuvers. Very hard to find.
1943 Sicily Sketch Book Published in Palermo Italy. Also hard to find.
1944 Mud, Mules, and Mountains This particular one has a blue cover, but I have seen other colors used. Perhaps they did runs of the book and when they ran out of one color, switched to another. These can be found without too much trouble online.