• WebElements
• NetElements
• Visual Periodic Table (RSC)
• Los Alamos Periodic Table
• Chemicool Periodic Table (MIT)
• Periodictable.com
• CRC Press Periodic Table
• Animated Periodic Table
• Periodic Table of Videos (Nottingham)
• American Elements
• NIST Data on Elements
• Chemical Elements.com
• Physics 2000 (U. Colorado)
• Enhanced NMR Periodic Table (Texas A&M)
• Touchspin.com
• ChemGlobe
• Periodic Spiral
• X-ray Properties of Elements (Illinois Inst. Tech.)
• Yahoo
• History of Chemical Elements (Brookhaven NL)
• Elements Database (K-12)
• Periodic Table of Comic Books (Univ. of Kentucky)
• NuDat (Brookhaven NL)
• Table of Isotopes (Lawrence Berkeley Laboratory)
• KAERI Table of Nuclides (Korea)

See also the pathfinder on General Chemistry.