I found a really nice free chess database online. It’s 365chess.com.
The site boasts a 3.5-million game database, which is regularly updated. It has several nice search functions The site has a very clean appearance and the interface works very well. Registration is free, though registration is required to search the database.
You can search the database by player names, by a particular board position, or using the opening explorer.
The one down-side is that you must be a “supporter” (i.e., pay for the service) in order to download games as pgn files. The up-side is that the service costs only $10.00 per year. Very inexpensive database!
Overall, the site is very nice and can allow you to do a lot of opening analysis for free.