The first ten books can be seen here. The second ten are here. Nos. 21–54 are below this post.
55. Ellen Raskin, The Westing Game (1978) (10/17/16)
It's a kids' book: it won the Newbery Medal in 1979. It's clever, and quite silly. It's also like a cartoon: most of the characters are strictly two-dimensional, and it's slapstick in the frenzy of the action, with scenes careening now right, now left. In the end, the various clues—involving "America the Beautiful" and chess, fireworks and the cardinal directions, a limp and disguises—add up pretty well, and everyone involved finds their own measure of success and happiness.
The winningest character is thirteen-year-old Turtle, aka Tabitha-Ruth, aka Alice. She kicks people in the shin, protecting her personal space (and creating quite a few limps); she suffers from being in the shadow of her lovely older sister, Angela; she's a whiz at the stock market. And it is she, in the end, who solves the ultimate puzzle—and never tells a soul.