Here are some great websites and databases on the net where you can get all the free guitar music that you could ever want.  You need to know some basics about reading tablature and chord progressions, but that's easy enough to understand.

Olga.net - Probably the oldest and best databases on the net...tons of free guitar tab here.

Guitar Tab Universe - It seems like they share a similar database with Olga, but its always good to have a second site that has the database of songs.

Guitar Tabs - A nice collection of guitar tabs here.

Fast Tabs - This is more of a search engine that will quickly search a bunch of other websites for tabs.

Christian Guitar Resource - A good size collection of religious type guitar music.

Classical Guitar Tablature - Its hard to find classical tab online and this is the best resource I've come across so far.