"Yaji Ash-Shuthath," meaning "There is no peace at the gates".
It was an All-in-One and One-in-All of limitless being and self — not merely a thing of one Space-Time continuum, but allied to the ultimate animating essence of existence's whole unbounded sweep — the last, utter sweep which has no confines and which outreaches fancy and mathematics alike. It was perhaps that which certain secret cults of earth have whispered of as YOG-SOTHOTH, and which has been a deity under other names; that which the crustaceans of Yuggoth worship as the Beyond-One, and which the vaporous brains of the spiral nebulae know by an untranslatable Sign...
Did we forget "Q" and the "Continuum" ? What a guy, or is this other Star Trek?
Of course the Ancients and Old Ones, but they're gone some way or another.
Evolve, travel away(leave), die out.
The Continuum is indelible ink, always there.
I've gotta go with the Aliens - you never really get to understand WHY they're killing; instead, you just get the impression that they're killing out of instinct, and you can't reason with instinct.
Plus, between the Alien Queen in "Aliens" and now that badazz Predalien in "Alien vs. Predator: Requiem", they've just got some of the coolest "super-baddies" around!
No B5 aliens listed? Oh dear, that makes it difficult. Personally I foind myself torn on this - my favourite B5 entity was Kosh. His enigmatic utterances took some unravelling but were usually straight to the point. My favourite B5 utterance - G'Kar's famous "No one here is exactly as they seem."
I presume that the Federation is the Star Trek Federation. If it is I vote for the Federation because it is what humanity should evolve to if it doesn't self-destruct in the mean time.