My parents bought a set of World Book when my sister and I were in elementary school. It might be the most important purchase they ever made for our education, as it not only helped with our information gathering for reports and whatnot, but was entertainment for us when bored. We loved just hopping into a random page and reading about whatever that thing was. It made me the info-junkie I am today, I think.

This has got me thinking about buying a set for my friends with kids (I'll check with them first and see if they have the shelf real estate).