Imp (beta name: Skirmisher) - A great unit. Powerful close-range ground-to-ground flamethrowers, and disguising themselves as the enemy facion are their specialties (they are often called Infils, to specify an Infiltrating Imp). Great for poccing, since, when disguised, they can still poc, unlike cloaking. Enemy units will not automatically attack disguised Imps, but they can be targeted by just right-clicking on them. Arabelsts will never attack a disguised Imp, making them even better for poccing. Unfortunately, they are not fast, and can't wear very good armor, due to low space and weight. Great for any type of hero. Education chars can have VERY dangerous Imps. Remember: Imp flamethrowers are effected by armor just like other weapons.
Daeva (beta name: Javelin) - Upgraded Imps. They're specialty is grenedes. Some people use them. I'm not too impressed with them, but I really don't know too much about them.
Mephit - Another type of upgraded Imp. Very cool looking, powerful ground-to-ground weapons, tough, and slow. I haven't had the chance to try them yet, but I definately will when I have the chance.
Shade - Some of the weakest units, but stil popular, since they are fast, and versatile in both movement speed and attack speed. They're weak because their weapons don't do as much damage over time as others, and become much weaker against armored units than other units would. Only good for Education characters, who can get cloaker shades, with the better laser weapons.
Banshee - Non-versatile shades. Much better, and more popular, but still not too great.
Phantom - Shades with even less damage, but armor piercing on all attacks. They were recently enhanced a LOT, because they were so bad, but they're still not very good.
Ghast - Fast melee units that are not very tough, but they get lightsabers! Their weapons attack quickly, with high damage, but they're melee, and not very tough. Some people use them so they can upgrade them to Revenants.
Revenant - Slow melee units that are very tough, and get the Earthquake ability. Earthquake does damage to everything in the area, kind of like Arbalests. They're also very dangerous with their normal attacks. Good for Clout characters, who can make them tougher.
Wraith - Extremely tough, extremely slow, and almost decent ground-to-air weapons. Clout characters with high Mk Wraiths can be very tough. But, they're so slow, and do too little damage, so few people use them, or just use them to upgrade them to Spectres or Liches.
Spectre - Okay ground-to-air weapons, and the ability to nuke. Quite popular units, particularly with Education characters.
Liche - Good ground-to-air weapons, and the ability to stop nukes. Not quite as popular as Spectres, but they're somewhat popular. The Infantry answer to Manticores.
Sapper - Sappers lay mines, and can cause great problems for people trying to poc, if they mine around a poc well enough. Sapper mines cannot be seen by enemies.
Medic - Medics heal your units, it's that simple. They can also cloak, or can get bio-scramblers (the Mind Warp ability), but better than the spirit version (3x effectiveness, but at 3x cost). Some people will bring a cloaker medic with them to heal their units during battle, hoping the enemy won't see them. Some people bring two cloaker medics, so they can heal each other. Two bio-scrambler medics can also work well.
Poda/Kritsk/Mlortha - Melee units that aren't too slow, particularly when they evolve highly. Can be really good poccers for a Clout character, due to massive HP.
Oizys/Boreas/Eris/Lyssa - Very fast air-to-ground, with good damage, but very low range. Good for Tactics characters. Not very good HP, especially as far as organic units go.
Ubik/Tyr/Haltyr - Tough units with a powerful versatile attack. Easily the most popular organic, and with good reason. Great for Education characters.
Slanth/Crudgin/Rouke - Not as tough as Ubiks/Tyrs/Haltyrs, but they do more damage, faster, over much more range, but they can't attack air. The second most popular organic unit.