Free Guitar Music

The Classical Guitar School, Iceland
Petrucci Music Library - a huge resource for out-of-copyright music generally - look for a guitar composer and see what's there.
Jonas Mollberg - many free original solo and ensembles - certainly worth looking into. - Some free sheet music, music lessons and resources for piano, guitar, flute, violin and other instruments. Free public domain sheet music of all categories, easy to find by composer, style or instrument.

Guitar Home Pages

York Guitar Quartet - my favourite quartet - well it would be, wouldn't it?!
York Classical Guitar Society - for all York (and other) lovers of the classical guitar of any standard.
Andrés Villamil - composer and arranger with a Columbian accent.
Classical Guitar Forum
The Classical Guitar Home Page
Cambridge Guitar Orchestra
Derek Hasted Guitar Ensemble & Guitar Orchestra
Early Music - Classical Guitar Ensemble Jon Sayles' page of a vast collection of free mp3 recordings of early music ensemble arrangements. An excellent resource.
GuitarBurst - a site with a large searchable database of guitar music, with grading, composers, publishers and more information.
The Guitar School - a lot of music by Eythor Thorlaksson for the classical guitar.
London Guitar Institute - offers excellent guitar education for all levels – from absolute beginners to very advanced guitar students.
Midland Fretted Orchestra
Modern Guitar Ensemble - an excellent blog resource for guitar ensemble information and interviews.
Ralf Bauer-Mörkens - composer - have a listen to some fine sounds here.

Other Guitar Publishers

Araniti Foundation - The Araniti Foundation is the first e-book publisher of guitar music in the world.
Les Éditions Doberman-Yppan (Guitar solos, duets, trios, quartets, guitar ensembles, chamber music)

Other Music Home Pages 

I Trovieri - An Italian school and ensemble with a good sound.

Guitar shops

London Guitar Studio - where I bought my Yulong Guo!
Gifted Musician - Music gifts for musicians and for people who are passionate about music
Stafford Classical Guitar Centre - guitars by many of the world's most talented luthiers