The people at about.com have kindly provided us with a list of free piano sheet music which can be downloaded and printed out.
The interface is a bit clumsy as you have to print out each page separately but as a way to get completely free and legal sheet music its not that bad. If you subscribe to 8notes.com (the providers of the sheet music) then you can download the entire scores in one go.
Included in the list of free music is:
Enjoy this free piano for beginners sheet music courtesy of about.com and 8notes.com