Guitar Soundfont Central
Soundfonts enable you to get the most realistic MIDI sounds from sound cards that support them. Includes information about installation, problem solving, and soundfont library.
MIDI Guitar Unofficial Home Page
Introduction to MIDI guitar, equipment needed, FAQ, and mailing list.
Ralphie's Home Site
MIDI files, instructions, MP3s, FAQ, and links.
Starr Labs
MIDI guitars, custom controllers, guitar electronics and accessories.