Terran Air Units

Dropship
Just like the Protoss shuttle it can carry your ground units wherever you want them. Heavily armored with no offensive weaponry so don't send them into a pitched battle.

Weapon: NONE
Domain: Air
Range: N/A

Wraith:
The best of the Terran air units. It can cloak when attacking so the enemy can not kill it. It has missiles for other air forces and a laser for things on the ground. It can cloak itself for attacks on units, usually not effective on other bases because they usually are
equipped with detectors.

Weapon: Laser and Missiles
Domain: Air
Range: Normal

Science Vessel
I never saw any real use for these except for their ability to detect hidden units. Though recently I have learned that their Irradiate ability is rather useful in killing enemy ground units. And that the EMP shockwave can easily make protoss units weak.

Weapon: Detector and Magic
Domain: Air and ground
Range: N/A

Battlecruiser
The biggest (though certainly not the best) unit in the Terran arsenal, although the Yamato Gun does considerable damage it can only be used once every 5 or 10 minutes. Also the Yamato takes time to charge up and leaves the Battlecruiser open for attack.
The Yamato gun though, is very powerful and has the longest range of the whole StarCraft game, the only disadvantage about it is that its site is not as long as it's range, therefore it cannot target as long, but if you scanner sweep the area you want to attack first then the battlecruiser could easily take it out.

Weapon: Laser Blaster and Yamato Gun
Domain: Air and ground
Range: Normal (Laser Blaster) Extra Extremely Far