Music reading skills and sightreading are a fundamental skill for all guitarists/musicians nowadays. Not only it is necessary to have a deeper understanding of your instrument, but it is a great way to share your music, and get good paying gigs (trust me, there aren't may well rounded guitarists out there that can sightread very well nowaday). These are five great resource sites that will help you with your music notation reading skills.
1. Practicesightreading.com
this is a great site where you can automatically generate measures of rhythm, in different levels. I feel this is a fantastic tool to challenge yourself, regardless of your level.
http://www.practicesightreading.com/index.php
2. Fretboard note finder
this is a great little page where you can find out where the notes are on a guitar tuned in standard tuning. When you click on a fret they show up on the upper right corner of the screen in standard notation.
http://www.eythorsson.com/en/Fretboard.aspx
3. Statens Musik Bibliotek
A collection of music pieces from the music Library of Sweden. The only way to improve your reading and sightreading skills is to read new material every day.
http://www.muslib.se/ebibliotek/boije/indexeng.htm
4. International Music Score Library Project
Same as above…more scores!
5. On sightreading music for guitar players
A fun articles about sightreading and why learning traditional notation is more important than tabs.
http://keithmoore1.wordpress.com/2008/08/11/sight-reading-music-for-guitar-players/