TheSupafly My brother has a bunch of these, I have no idea where they came from originally but he got them as a gift. They are pretty nice.
cognitivedissonance The Old West, Unexplained Mysteries and The Magical World got me through ages 10 to 14. I loved every Time-Life series they made, and grown-up me often considers buying them when they come up on eBay.
Caminante Nocturno My high school library had the entire Time-Life series collections, and I read every single one. They were amazing books.