KIRK:
Kirk's middle initial / middle name. It is generally agreed that Kirk's full name is "James Tiberius Kirk". It was only given as "James T. Kirk" in TOS, the "Tiberius" didn't come around until TAS ("Bem") and the novels. It was formally established in ST6. In Where No Man Has Gone Before, Gary Mitchell makes a gravestone for Kirk that says "James R. Kirk", apparently before Gene had settled on a middle name (or possibly proof that Gary was failing as a god).

SPOCK:
Spock's other name (you couldn't pronounce it, as he told the blonde in This Side of Paradise) isn't given in TOS or TFS. It is given in one or more of the books if you care to believe them. According to the Officer's Manual (and probably originated from D.C. Fontana), it is Xtmprszntwlfd (pronounced with six syllables). In the novel "Ishmael", it is given as S'chin T'gai.
In Journey to Babel there's this exchange:
Kirk: Mrs. Sarek...
Amanda: Amanda. I'm afraid you [can't?] pronounce the Vulcan form.
Kirk: Can you?
Amanda: In a fashion, after many years of practice.

MCCOY
McCoy's middle initial is given in Friday's Child and The Search For Spock as "H". Some novels have it as "H", others as "T", and apparently still other have his middle name as "Edward". Geoffrey Mandel's Officer's Manual lists his middle name as Horatio.

DATA
Data's name was shown on a computer screen (in The Measure of a Man) as "Lt. Cmdr NFN NMI Data" ("No First Name, No Middle Initial").

Prošli tjedan sam diskutirao sa Nightshootom oko Datinog imena i poslao mi je url http://www.moviemistakes.com/tv3008/trivia gdje se spominje da se u TNG epizodi "The measure of a man" vidi NFN NMI Data na displayu kad Riker pregledava Datine podatke za potrebe saslušanja o Datinim pravima. Nakon što sam to pročitao, pogledao sam epizodu. Kad Riker pregledava podatke, iz naše perspektive display je mutan i tekst se uopće ne može razaznati, niti jedno slovo, a kamoli NFN NMI Data.

jesi siguran da ne vidis to zbog kvalitete tvoje snimke?

U divx-u je i kvaliteta je ok. Stvar je perspektive gledanja, ne kvalitete.

EDIT
Što se Spocka tiče, nekanonski izvor Memory Beta navodi oba imena koja je Chaky spomenuo.
http://startrek.wikia.com/wiki/Spock