Sobol was a prolific author, writing daily even to his last days. Encyclopedia Brown is his most famous work, but I have fond memories of reading his novel Secret Agents Four. This is a tale of four Florida teenagers who, in league with the good-guys spy agency Mongoose, form their own secret spy group to bust the evil Cobra. V.A.C.U.U.M. (Volunteer Agents Cruising Unsteadily Under Mongoose) and their pal Mary (V.A.C.U.U.M.'s Beautiful Assistant Girl) have to use a garageful of Rube Goldberg inventions and antique cars to foil Cobra's evil plots to take over Miami. I haven't read it for years, but I remember it being funny, suspenseful, and charming.
And of course no discussion of Sobol's books would be complete without mentioning the iconic illustrations of Leonard Shortall.
RIP, Mr. Sobol.