Command and Conquer Gold
Downloading and installing the game may take a little effort, however. EA no longer hosts the files, which are too large for the PC World download site. Instead, EA suggests downloading the files from sites such as Fileplanet.com, which is where the above Download link will take you.
Also, the files are in .iso format, so you'll need to burn the files to cd and follow the instructions (still available from EA) to install.
More effort than the usual download to be sure, but if you're nostalgic for a classic game it's a nice free option.