dougie_monty: Your first is the notes of the scale. Your second is the grades on a report card. Your fourth, I believe, is The Phone Company Alphabet.
To the OP: you are driving me crazy. Give it up.
Alright, I haven’t worked it out, but I know what the clue in the OP is - the title. Complete the series. One letter must complete the series. So the whole series has seven letters. It could be the initials of all the elements of a set with seven elements, like the days of the week. I flipped through the U’s of my dictionary, though, and didn’t come up with anything.
Oh my lord, the guy’s a trekkie.
It ©hekov.
What a complete waste of time.
Not exactly a series, not really, no. Frowny smile here.
Scotty comes before Sulu, anyway.
To Masonite: You guessed right. 
The third is chemical-element symbols that are single letters (boron, carbon, fluorine, etc.).
The last two are one-letter movie titles (I am not a movie fan; other Dopers may know of others), and computer drives (I once posted a thread about the omission of the B: drive.) 
Well, if it was the characters of Star Trek, I challenge the word “logical” to describe the sequence. For one, it relies on knowing trivia rather than logic, and the order of characters does not conform to their ranks or the order in which they first appeared in the series.
Logical was a reference to Spock.
FTR, I worked out the answer by looking at the OP’s posting history.
It’s pointless arguing sense or real logic now.
Well done to Desmostylus, who applied research when first principles failed.
Who the hell made you play? What exactly would make a “next in the series” brainteaser a good use of your time?
That was a joke Bob Cos.
I needed to work the word “complete” into the answer. 
What the heck Bob Cos, pit me.
The “logical” reference was already explained.
Moreover, the ordering DOES conform to their ranks. The characters were listed in descending order of their ranks in the original series. This provides a logical pattern to their ordering. (Kirk was a captian, Spock was a commander, Bones and Scotty were lt. commanders, Sulu and Uhura were lieutenants, and poor Chekov was a lowly ensign.)
Howz about…
M V E M J S ? ? ?
D D P V C C ? ?
A B D G K ? ?
UNP
?
P
UNP
?
PV
Oops. Sorry.
Ah, but if McCoy/Scott and Sulu/Uhura are of the same rank, then you had to make an arbitrary (as opposed to logical) ordering decision. Your sequence could have been expressed four different ways, which makes it unsuitable as a logic puzzle.
[sub]nitpick ME, would you?[/sub]