(Click for bigger!)
The one above (published July 21, 1969 and April 7, 1977) is particularly masterful, featuring a kind of criss-cross composition, where Nancy/Rollo get smaller and lower in the second panel, while the well gets larger and higher, stopping the eyes and emphasizing the end of the gag. I love the subtlety and economy of how just one small detail, the handle, indicates that the figures have moved to the other side of the well. The drawings are, of course, immaculate. Here are some details:
I also love the character Rollo, the rich kid. He wasn't like Ritchie Rich or other cartoon rich kids. Bushmiller didn't usually use the character to make jokes about wealth per se, but to lampoon the wealthy's taste for modernism in all its pricey forms (incomprehensible modern art, uncomfortable modernist furniture, etc.). In one strip, Rollo tells Nancy that his family is going to have a "real old-fashioned Christmas" just before revealing their cubist, abstract Christmas tree.
Next up is the drawing for the strip published on June 13, 1969 and June 29, 1977:
(Clicker for bigger.)
Fantagraphics calls the 1940s and 50s Bushmiller's "classic years", but to me it's his 60s strips, so minimalist and precise, which are his strongest work, although perhaps less easy to appreciate because they're so barren. It's almost as if, in the 50s, he became the Mondrian of cartoonists, and then in the 60s, the Barnett Newman of the medium.