In this blog entry I've added all officially confirmed third degree Protocol and Service Droids that appear in the Saga.

- 3PO Droids: Protocol Droids built by Cybot Galactica
- BD3000 Droids: Luxury servant Droid built by Leisuremech Enterprises
- CZ Droids: Communications / business Droids built by Serv-O-Droid.
- LOM Droid: Insectoid Protocol Droid built by Industrial Automaton.
- RA Droids: Servant / spy Droids built by Arakyd Industries
- TC Droids: Protocol Droids, almost similar to the 3PO models
- WA Droid: Servant Droid

Appearing in all movies of course is C-3PO.

The Phantom Menace
TC-14: Silver Protocol Droid served the Jedi aboard the Saak'ak.
TC-3: Silver Protocol Droid served the Swokes Swokes delegation in the Senate. Picture in 'Chronicles Prequels'.
TC-4: Red Protocol Droid served Senator Palpatine.
Nobot: Ghost Droid that walked at Mos Espa.
Unknown Protocol 2: Was standing lifeless in Watto's shop.
Unknown Protocol 3: Was seen on pictures with the Twi'lek delegation.

Attack of the Clones
WA-7: burly waitress Droid at Dex's Diner.

Revenge of the Sith
Three BD-3000 units were present when Palpatine returned safely to Coruscant.
This grey BD-3000 unit worked in Bail Organa's office.
This blue BD-3000 unit was seen at the Galaxies Opera House.
This silver Protocol Droid was present when Palpatine returned safely to Coruscant. Picture see above.
This matte grey Protocol Droid was present when Palpatine returned safely to Coruscant. Picture see above.

A New Hope
U-3PO: Protocol Droid seen at the Tantive IV. Unbeknownst to itself, it was espionage Droid of the Empire.
CZ-1: This communications Droid was sitting lifeless in the Jawa Sandcrawler. Formerly known as CZ-OR6.
CZ-3: This former partner of CZ-1 wondered around on Mos Eisley when Luke sold his X-34.
3B6-RA-7: This silver model was found on the Jawa Sandcrawler and 'welcomed' Artoo.
5DK RA-7: This black RA-7 model was walking in the Death Star when Luke and Han were about to rescue Princess Leia. Received his name in 'The action Figure Archive.
QT-3PO: This Protocol Droid was found in the Sandcrawler and had a huge hole in its head.

5D6-RA-7: Was a black RA-7 unit assigned to Motti on the st Death Star. It had a decipher card where it was seen near a lift tube. This could very well be the same Droid as 5DK RA-7. Then, two sources would have conflicting information (Decipher and Action Figure Archive).

The Empire Strikes Back
K-3PO: This white Protocol Droid was seen at the Echo Base command center.
R-3PO: This dark red Protocol Droid was seen at the Echo Base hangar.
E-3PO: This silver burly Protocol Droid greeted Threepio on Bespin with 'E Chu Ta'.
4-LOM: This former Protocol Droid was one of the Bounty Hunters summoned by Vader on the Executor.
Unknown Protocol 1: Was also seen at the Echo Base hangar.
Unknown Protocol 2: Was seen at Cloud City when Lando brought his guests to Vader.

Return of the Jedi
CZ-3: Was seen in Jabba's droid Dungeon in pieces.
CZ-4: Was seen in Jabba's courtroom when Han & co are convicted to the Sarlacc.
Unknown Protocol(?): this 'protocol droid' (?) was tortured in Jabba's droid dungeon. Often receives a fanmade name.

If you know any other officially confirmed Droids that appear in the movies, please let me know.