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Droids, are numerous types of  robot depicted in the George Lucas Star Wars films: The Phantom Menace, A New Hope, The Empire Strikes Back and Return of the Jedi, and in the many Star Wars books. Droids possess intelligence and mobility to varying degrees, dependent on function. 
There are many manufactures of droids; the two dominant players being Cybot Galactica and Industrial Automation. 

Droids I've discovered so far:

Model type 

Description

Astromechanic droids Products of Industrial Automation within the Star Wars universe. The astromechanic droid series include: P2, R1, R2, R3, R4, R5, R6 and R7. These droids specialize in starship diagnostic and repair. Astromech droids are designed to operate in hostile environments and are expert in computer repair and information retrieval. Of course the most famous astromech of all is little  R2-D2.

2-1B

The grey coloured 2-1B is a highly talented surgical droid, manufactured by Industrial Automation & Geentech
3D-4X Manufactured Genetech
3PO Protocol droid Truly an android with human like appearance, the 3-PO series droids are manufactured by Cybot Galactica. Very complex neural network brains allow these droids to act as interpreters and diplomats. 3-PO units are conversant in over 6 million languages and expert in customs, etiquette and the religions of many species. Cognitive skills and pattern analysis allow them to translate unknown languages. see C-3PO.
4-LOM The LOM series of protocol droids are remarkably similar to the 3PO series, except for their 'insectoid' head. LOM droids where manufactured by Industrial Automation after a little industrial espionage against Cybot Galactica. The 4-LOM droid variants went rogue and became bounty hunters. A 4-LOM droid was contracted by Darth Vader to find the Millennium Falcon.
Battle droids Centrally controlled military droids used by the Trade federation in 'The Phantom Menace' 
B'Omarr Monk B'omarr monks seek enlightenment by inner contemplation. Their brain and mind, freed from the physical body, are placed into nutrient liquid and contained in a jar. To move about; the brain is inserted into a shatterproof glassine 'bulb' suspended below a Spider like machine. B'omarr monks are therefore cyborg in nature.
C-3PO This shaky, naked, bundle of wires 3-PO unit was home-built by the young Anakin Skywalker in 'The Phantom Menace'. In Later films C-3PO gained a shiny gold skin and a little side-kick called R2-D2. 
CZ - OR6 A Secretary / communications droid manufactured by Serv-O-Droid. CZ units are outdated but make excellent couriers since they possess advanced encryption algorithms for storing files.
Destroyer droids -  Elite military units of the Trade Federation seen in episode 1 - 'The Phantom Menace'. Destroyer droids are folded into a wheel shape for speedy deployment, but swiftly turn into high power weapon platforms complete with deflector shield.
EG-6 Power droid Mobile power generator manufactured by Veril Line Systems. The EG-6 unit is a  walking fusion generator in the shape of a black box. This droid has limited language capability but is capable of running sophisticated diagnostics before allowing power transfer to ships, vehicles or droids. It does have a small arm for delicate work.
EV-9D9 supervisor droid EV series droids where manufactured by MerenData for the middle management of other droid workers. EV droids possessed female cognitive brains, but due to a 'cock up' they were programmed with torture droid motivators; causing them to be sadistic and sometimes psychotic ("sounds about right"). Although all were recalled by the manufacturer, several are still at large. EV-9D9 worked for Jabba the Hutte before being destroyed by one of her previous employees.
FX-7  medical assistant droid Mulilti-armed medical assistant, constructed by Medtech Industries and designed to aid surgeons.This droid had scanning devices, monitor screens and medical diagnostic capabilities. the unit was fixed in place but could rotate. Much older than 2-1B.
 IG 88 IG series droids where created by Holowan scientists specifically for use as assassins. The 2 metre tall IG88 is one of only five renegade IGs whom all act as bounty hunters. IGs are armed to the teeth with; blaster cannons, a grenade launcher, a flamethrower and poison gas canisters.
IT-O Interrogation droid Horrifying black spheres produced by the Empire to extract information from prisoners by any means. Interrogation droids have pain inducing appendages and are trained in medical, psychological and surgical techniques. This droid was used unsuccesfully, by Darth Vader, in an attempt to extract information from Princess Leia in 'A New Hope'. 
Pit droid  episode 1
R1-G4 Ancient, black, Astromech droid found by the Jawa scavengers. The R1 series had a single leg with caterpillar tread. This droid was the first to be fitted with radiation shielding and had the ability to speak in the now familiar whistle and beep language associated with newer Astromech droids; also the first R unit to be capable of calculating  hyperspace co-ordinates. (The protrusion is an antenna not a gun)
R2-D2 This Famous Astromech droid first showed of his features in the film 'A New Hope': Holographic projector, Arc welder, circular saw, etc the white, R2 unit was plugged into the rear compartment of rebel X-wing and Y-wing fighters. The R2 units are still in production thanks to this little droids tenacious actions.
R5-D4 Cheap R series utility droid that, although mass produced, never really made it. See Astromech droids.

Manufacturers of Star Wars Droids:

Accutronics Industrial Automation Rebel Allienc
Arakyd Industries LeisureMech Enterprises Roche
Balmorran Arms Les Tech Serv-O-Droid
Corellian Engineering Corp Loronar Corp Sienar Intelligence Systems
Corporate Sector Authority Lovalon SoroSuub Corp
Cybot Galactica Meditech Industries Telbrintel
Geentech & Genetech Corp MerenData Trang Robotics
Go-Corp(Utilitech) PowerPost Ulban Arms
Holowan Mechanicals Publictechnic Veril Line Systems
Imperial Dept of Military Research Rebaxon Columni