Many many various units. When I finally get somewhere high in the areas of tech my list of units I can build tends to be humongous..!
I'll see if I can scour my mind for a few of the favourites. Some are just cool, others interesting, others mighty and some purpose-fitting.
Militia - infantry, hand weapons, next best armor available, clean reactor = No support and relatively short building times, just crank 'em out in high numbers and watch the enemy offensives get bogged down.
All-terrain formers - gravship, terraforming unit, low-level armor, best available terraforming specials = Quick moving terraformers capable of dealing both with land and sea forming.
Suicide Squad - infantry, mid-level weapon, mid-level armor, clean reactor, possibly drop pods = Non-supported troops built only for one purpose... Mass-dying against enemy installations.
Naval probe team - cruiser, probe equipment, low-level ( if any ) armor = Fast moving probes for shady sea operations.
Mindworm Annihilator - needlejet or gravship, hand weapons, low-level ( if any ) armor, empath ( or is it trance? The one for attacking, in any case ) = Quick response flight capable of wiping the mindworms out before they cause trouble.
PSI corps - infantry, PSI-attack, PSI-defense, high morale, possibly drop-pods = When dealing with an enemy faction supporting largely low-morale troops train these units in cities with lot's of morale improvements and watch them annihilate the enemy weaklings.
Medical craft - needlejet, chopper or gravship, transporting unit, mid-level armor, medical ( repair? ) bay = Aircraft designed to swoop in, pick up overly wounded/damaged units and fly them back to "safety" whilst repairing/trating said units.
Then of course there are all kinds of silly experiments I tend to from now and then. Some work, some don't. I probably could keep going on for a looong time with this. But I won't... <img src="tongue.gif" border="0">
Cheers!