Free FULL LEGAL games - C&C1, FarCry, Ghost Recon, PoP

[EvaUnit02]

Command & Conquer 1
A quick Google search brings up these mirrors of the two ISOs (one is the GDI disc, other is the Nod disc).
http://www.gamershell.com/download_20863.shtml
http://www.gamershell.com/download_20864.shtml
More mirrors of GDI iso.
More mirrors of Nod iso.

If it's anything like the Red Alert 1 installer:- You'll probably need to run the installer in Win95 compatibility mode. Plus it might not work under x64 Windows because it'll highly likely have a 16-bit installer.

Far Cry - ads in the main menu, none in-game.
Mirrors
x64 Windows support requires like 2GB worth of patches, which I bet won't work with this ad-sponsored version.

Ghost Recon - ad-sponored

Prince of Persia: Sands of Time - ad sponsored. I heard that this one is a bad PC port though.

All these ad-sponsored games require Ubi.com US account, as it's US only content.

EDIT - HAHA:-
You can also play multiplayer, I believe (didn't try it). I had to stop playing and uninstall them because the McDonald's commercial at every possible load scene got way too frustrating.

It would've been fine if the game loaded while the commercial was playing, but the game stops loading, the commercial plays, then the game continues to load... Good idea, but way too much.