EnvironmentalChemistry.com: Seaborgium
Atomic structure and table of nuclides.
It's Elemental: Seaborgium
Basic physical and historical information.
Lenntech: Seaborgium
Physical data and chemical properties.
Visual Elements: Seaborgium
Physical information, ionisation energies, and key isotopes.
WebElements: Seaborgium
Information on history, isolation, and properties.
Wikipedia: Seaborgium
History and basic information on the element.