The Sequel to E. D. Hirsch, Jr.'s book, Culural Literacy: What Every American
Needs to Know, this book is a dictionary of terms that are frequently referenced in everyday American culture. Everything from people (Richard the Lion Hearted, Rube Goldberg), places (Golden Gate Bridge, Timbuktu), ideas (poll tax, confirmation hearings) and things (Molotov Cocktail, meteor).
You can buy the book at Amazon.com, and they periodically (yearly?) release new editions. It's a great book to own, and I highly recommend it.
This book is great for any uninspired factual noder. Many of the examples I gave aren't nodes, and yet would make great nodes to add to the E2 universe. If you want to make factuals, and you're stumped for ideas, the Dictionary is a great place to start.