I'm not sure if this has been posted before, but, for the next thirty days, you can download several of the older games in the Command & Conquer series for free at http://www.commandandconquer.com/classic
Command & Conquer (both GDI and NOD sides)
Command & Conquer: Red Alert (both Allied and Soviet sides)
Command & Conquer: Tiberian Sun
The domain appears to be owned by Electronic Arts so I would think that this is a legit promotion.