Interesting sites for guitar players:

www.guitarraalacarta.com (lutherie guitars selling and accesories)
www.guitarfoundation.org
www.fernandosor.fr.st   (free download from all his works)
www.maurogiuliani.free.fr/en/  (free download from all his works)
www.guitarristas.com (forums, news, sheet music, etc.)

USA luthier websites:
(suggested for amateur and professionals builders)

www.luth.org
www.schrammguitars.com (huge information website)

Accesories websites:

www.vendoma.com.ar
www.luthiermusic.com
www.stewmac.com
www.lmii.com
www.stringsbymail.com
www.casaprado.net

Friends guitarist websites:

Javier Bravo
Juan Falú
German Herlein
Ariel Osuna
Sfriso - Ujaldon
Dúo Saldaña - Bravo
Claudio Ceccoli
Conde Larrosa
Ramos - Schneider
Szternstejn
Jorge Menezes
Marcos Puña
Sergio Moldavsky
Juan Gallino
Berta Rojas
Victor Villadangos