One of the most popular way guitarists learn how to play songs is through the use of tablature. This is an easy to understand form of music notation that shows exactly when and where each finger should go on the fretboard. Many guitar magazines include several songs tabbed-out which used to be a great way to build a library of song tabs to keep on hand for reference.
I stumbled upon a web site named Songsterr: http://www.songsterr.com
This service like an on-line version of Guitar Pro. While not quite as robust, the basic version is free! We're talking over 60,000 tabs from over 1500 artist. That should be enough to keep me busy for awhile! Don't get me wrong, I'm not dropping any magazine subscriptions - printed tab still has a place in the guitarist's learning arsenal, but this service is awesome.
Check 'em out!