e-resources from the Poudre Library District

http://www.poudrelibraries.org/eresources/
You need a Fort Collins Library card to access the databases, but this is literally an entire free online library of journals, articles, audiobooks, periodicals, and reference books. It includes searches from a wide range of publications, from Ranger Rick to Archaeology Today.

Google Books

http://books.google.com/
This is a great source for public domain works, literature and history before 1925. For example, click here for Machiavelli's "The Prince."

Khan Academy

http://www.khanacademy.org
Khan Academy provides a video library, interactive challenges, and assessments completely free of charge.