Rise of the Reds (rotr.game-mod.net) adds the Soviets into ZH, as well as some other additions. Also it should be released pretty soon. My mod Last Stand (
www.calcots.co.uk) also adds Russia, as well as the UK, but is far from finished. Red Dawn (reddawn.cnc-hq.de) is a mod tht adds the soviets as well, but I think it's been haulted. They have released betas tho, so you can still play it.
There are also all the HUNDREDS of Red Alert series total conversions, but as far as I know none of them have been released yet.