M. Delcamp has provided a series of links to other sites offering free sheet music which respect copyright. You can find these by following 'links' on his front-page http://www.delcamp.net/liens/pdf.htm
Most other sites do not grade music by level, except Eythorsson's Guitar School Iceland which grades many scores in the catalouge section and Dirk's Guitar page which grades some scores. Minami and Richard Yates have mostly more advanced scores on their sites, Dos Amigos has a high proportion of easy to intermediate scores. Most other sites have a mix of pieces from easy to advanced.
Eythorsson and Jan-Olof Eriksson have scores for 2, 3 and 4 guitars
I've locked this thread to stop anyone inadvertently giving links to other sites which do not respect copyright - there are unfortunately many of those, and moderators often don't have time to check them out.