i also play NOD
a tactic that i found works great (and pisses off your opponent) is to build the following:
crane
2 refineries
2 powerplants
1 war factory & one command center
you then build 3-4 flametanks. you drive them near the enemy base and cloak them in the stealth field (which costs 3000 but it's worth it). you then drive the cloaked flame tanks into his base, taking out his crane and any tech buildings he has. flame tanks work better against buildings than even mammoths, but they have weak armor so they must be cloaked when you do this.
at the same time you continue building buggies and scorpions, and send them in to finish him off once your flame tanks have been destroyed.
i have yet to find a working defense against the stupid GDI pitbull rush, though.