The Pedal Steel Pages No sheet music, but lots of articles and discussions (E9th theory, tunings, etc) on pedal steel matters
Richard Yates' Classical Guitar Transcriptions Richard Yates's site (He has a Classical Guitar book published by Mel Bay). PDF's to MANY wonderful classical pieces -- also, MIDI's for a bunch of them. Richard also asks for reader feedback -- for instance, he's transcribed Pachelbel's Canon for a guitar duet because of viewer request. This page is a treasure!
John Sherman's Celtic Guitar Page "Celtic guitar, simply put, is that body of music arranged for guitar that includes the traditional musical repertoire of the Celtic regions of Europe (primarily Ireland and Scotland, but also including Wales, Brittany, the Isle of Man and Galicia) or that can claim to be influenced by it." Describes modal tuning, offers jpg's of sample tunes (hey, it's treble clef -- try it with your fiddle!)
Northumbrian Traditional Music Fiddle, Guitar, and Song! Sheet music, tabs, and ABC's of "the unique traditional music of Northumbria, an area encompassing the modern counties of Durham, Tyne and Wear and Northumberland."
German Guitar Music German site, guitar music, many styles. Can't read German, but I think it's got classical, rock, jazz, and blues.
Matt's Music A number of tabs -- pretty cool looking site. Be aware that it creates a new browser in maximum mode without and address bar or a minimize or close button. I had to use "Alt-F4" to close it. Still, it's some nice work.
Free Sheet Music for Piano and Guitar You must register first (free); you'll then receive free access to a slew of standard notation (and guitar tab); lots of classical pieces, many traditional pieces and ethnic folk pieces too.
Discover The Guitar ! Homepage of classical guitar teacher Philip Castledine . Music available to download in both .pdf and .mp3 formats
Handcrafted Guitar Tablatures by Johnny Spaugh "I began tabbing classic guitar tablitures over twenty years ago tabbing songs for six string guitar. I have done all the work so now you can teach yourself and play old favorites from Old Time Fiddle Tunes, Gospel, Western Swing Instrumentals, and Old Country Songs (40's - 80's)." Mainly books for sale, but there are some nice free samples.
Guitar 33 - Free tabs and Scores About half a dozen free scores (including audio files) each month from French guitarists and composer, Michel Dalle Ave. Many different styles (classical, celtic, rock, blues, latin, fingerstyle, etc)
Musicalexx Good guitar tab and chord site. Nice touch is that the guitar tab is in .pdf format!
Guitar Alliance Riff-O-Matic Publishes four or five different cool riffs in tab format every week. Stevie Ray, Jimi, Randy Rhodes, etc. Also includes slow and fast audio files so you can hear how the riff should sound like.