Official Casio Sites:

Gshock.com – Official G-Shock USA site
Baby-g.com – Official Baby-G USA site
G-Shock.jp – Official G-Shock Japan site
G-Shock.eu – Official G-Shock Europe site
World G-Shock – Other official G-Shock sites
Official Pro Trek USA
ProTrek.com – Other official Pro Trek sites

Official Casio Support:

Select Country or Region for Support

G-Shock Replacement Parts:

PacParts (USA)
American Perfit (USA)
Tiktox (UK)