I put this up a while back (and need to update it): http://joemaller.com/1856/download-google-fonts/

Google changed repository layout so there are a lot more subfolders to sort through but `hg clone https://code.google.com/p/googlefontdirectory/` still works fine.

(edit: just saw @shadowmint's update, agreed about https://github.com/w0ng/googlefontdirectory being better in every way.)