As you may know, publishing lead sheets / tabs / chords of popular songs is a bit of a grey area legally.
Some guys from Belgium started the 'Wikifonia Foundation' and made a deal with the local copyright guys, which now allows them to legally publish community-submitted lead sheets on http://wikifonia.org/ .
Not sure how this works wrt international law, but they have accumulated a fair amount of material already. Interesting development.
Legal lead sheets
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