Build anywhere: 
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. 

Chronosphere:
Want to have some fun with the enemy player? Charge up the Cronosphere and use it on the enemy unit, then drop it in the water. Watch the war miner go down to the bottom! Bye bye. Also try it on ships and drop them on land. Killing an entire infantry group is fun since infantry can die under the effects of the Chronosphere. Go ahead, try it!

Iron Curtain:
The previous cheat refers to the Iron Curtain as well, fry those GI's!

Chrono Legionnaire (1):
Put one Chrono Legionnaire inside an Infantry Fighting Vehicle (IFV) to make a Chrono Fighting Vehicle. The Chrono Beam doesn't get any stronger, but your units won't die as easily.

Chrono Legionnaire (2):
Chrono Legionnaires packed together can even zap an enemy building out of time, try it. Ten Legionnaires and above give the maximum effect.

Libyan Cheat:
Build five or six demolition trucks. Make sure you have a fully charged Iron Curtain. Send the Trucks into an enemy base, before they come in range of their weapons, cast the Iron Curtain on them. They'll be invincible until they reach their target, at which point they'll still explode even with the Curtain on.

The Magic School Bus (Soviet):
Take a Yuri and mind control a school bus (if they're on the map). You can put five infantry into the Bus and drive it into an enemy base, they won't fire on it. You can also load up a bus-full of Engineers =)

Good Use of the V3:
If you play as the soviets, one of the best way to use the V3 Rocket is to have about 3 Rhino tanks for each V3 Rocket to protect them. If you have about 5 V3 Rockets and 12 - 15 Rhino tanks you can take out a medium base! One of the reasons is that the V3 Rocket fire very long!

Allied Advantage:
In Multiplayer or skirmish mode, use spies to infiltrate all enemy battle labs. This is to train new units like the physic commando (he can use the mind control and plant C-4 on buildings). Later, if you capture the base completely (meaning all buildings) you will get the Yuri Prime.

Excellent Base Defense:
Make 10-12 Yuris and place them all around your base. Put them as team1 (Ctrl + 1) then when an enemy attacks use the Yuri's 2nd attack. This should destroy most of the attacking force.