Others may have a good lead on large free databases available out there, but one thing you may also want to consider is paying a visit to the TWIC site every week to grab their free weekly digest of the latest and greatest games - available in PGN, text, and chessbase formats.
http://www.chess.co.uk/twic/twic.html
At a few thousand games a week, you build yourself up a decent sized repository of games pretty quick.
Hey, was just wondering if you guys knew of any good free chess databases softwares. I have Chessmaster 10, which offers a mediocre quality database so I tried to move to something better. I also just installed ChessBase Light 2009, which I find is alright. I don't know how it compares to the premium version though. What do you guys use?