I don't know of any free ones. Chess King, $27.95 from Amazon.com, last I looked, has an extensive GigaKing database, much more extensive than chess.com's Opening Explorer or chessgames.com's databases.
I'm no authority on databases so if you know of better free stuff than I list below, please post it here. The free stuff I know of includes:
Kingbase: 1.8 million elo 2000 or higher games since 1990 in pgn files:
http://www.kingbase-chess.net/
Million Base 2.2: a 2.2 million game pgn database is here:
http://www.top-5000.nl/pgn.htm
An extensive set of specific opening and player databases in pgn files is here:
http://www.pgnmentor.com/files.html
Can someone please post a website that gives a database of almost all chess games from around 1970 or earlier to now.