The Tato family of stools from Baleri Italia (Enrico Baleri & Denis Santachiarahese), are just plain fun.
Designed in 1995, they're "surprisingly comfortable" (we're quoting the Unica website here) due to a rigid internal plastic structure hiding underneath the soft, ecological foam rubber that makes the bumps so appealingly organic. The materials work together like memory foam, cradling the sitter's rump and then returning to their original shape when vacated.
The stretch wool or polyamide covers come in an array of happy colors, and they're kept in place with two lateral slits built in to each bump.
Available at Unica Home.