The People's Almanac by David Wallechinsky and Irving Wallace. He told me about it as I leafed through it. It was a randomly ordered collection of information and, I gradually realized, thinly veiled Communist propaganda. (The title was kind of a big hint.) My great uncle had apparently never realized this and had, in fact, used it for years to help my cousin write reports for school.
Little did I know at the time that The People's Almanac (and other books by the same crew, most chiefly The Book of Lists) were primary inspirations for John Hodgman's books. But I know it now because I listened to this interview Hodgman once did with Jesse Thorn on The Sound of Young America. In it, Hodgman talks about writing his first book, how writing his second book was a much different experience, and a few of his thoughts on his then-distant (now imminent!) third book.
Hodgman and Jesse Thorn also discuss Hodgman's emerging Judge John Hodgman routine (then just a segment on the Jordan, Jesse Go! podcast). Hodgman complains that they don't have enough cases!
I enjoyed this interview and recommend it. Again, you can find the mp3 of the interview here.