Command & Conquer Red Alert 2 Cheats

First of all you need to build the Cloning Vat. Then put walls around your primary barracks so that no infantry units can get out. Now build any Infantry unit, although the unit will be unable to come out and therefore you are refunded but the one out of the Cloning Vat will come out for free. {Note: This will not work if you have the 1.006 patch or Yuri's Revenge}

I think this works in all patches.
Build a cloning vats and capture a hospital. Hurt a infantry unit with another unit but don't kill it. Send the hurt unit into the hospital and when it comes out a free infantry will come out of the cloning vats.

Wait until you have paradrops AND a building ready to be placed on the map, then click on paradrops icon in the sidebar (but don't deploy them yet!), then click on your building (the one that's ready). Now simply use the mini map in the lower right corner to deploy your building.