Biodiversity Heritage Library - Natural history and botanical garden libraries' digital collections
HowStuffWorks - Credible, unbiased, and easy-to-understand explanations of how the world actually works.
Inventor Archive - Biographies of inventors
Online Conversion - Convert just about anything to anything else
Periodic Table of the Elements
Science360 Knowledge Network - Current science videos by leading researchers, sponsored by the National Science Foundation.
Science Daily - Breaking news about scientific discoveries