Gradius Army: Gradius artwork, information, and links.
Gradius Home World: Information about Konami's Gradius, Salamander, and Parodius games including screen shots, box scans, etc.
Planet Gradius: An older Gradius site with pictures, information on ships, release history, and emulation.
The Gradius Base: A new Gradius site with music and a great list of Gradius references in other games.