Origin's 'On the House Program' is offering Battlefield 1942 for free this month. The game is free to download and keep, no string attached - except that you have to install and use EA's digital distribution platform. Last month EA gave away Dead Space for free.
EA plans on continuing to release full games, expansions, and more at no cost for the foreseeable future.
If you like free stuff and don't mind installing Origin, then you can grab Battlefield 1942 from this link.