: TL;DR below if the stuff that follows this is irrelevant.

: I've searched mainly levels from Halo 2 (in my opinion, having housed the
: best dialogue in the franchise), as well as Halopedia (halopedia.org, not
: the other bastardized wiki) for other characters.

: I submitted "7here are those who said this day would never come, what
: have they to say now?", by Halo 2's Truth on the 4 April deadline,
: and told a friend the next day. He said that it would lead people to
: believe I wouldn't graduate, which is not the impression I want to leave
: as my high school career's legacy. Now that's a scary thought! (For the
: record, his is, "You see a mousetrap, I see free cheese and a fucking
: challenge.")

: So after some searching this weekend, I came up, tentatively, with:
: "Every Great Journey begins with a single step. This is our
: beginning." from the Halo 4 credits. I might end up putting a 7
: around there somewhere, I'm infamously well-known to teachers and students
: for 7ing up their lives, I'll just substitute it for a letter
: "t".

: Just some simple Googling came up with the B.net forums, which some people
: have already asked for quotations there. The problem I have with some
: quotations are that some are amazing, yet way too dark and eerie, not fit
: for graduation.

: "Silence fills the empty grave, now that I have gone, but my mind is not
: at rest for questions linger on."
: "If they came to hear me beg, they will be disappointed."

: Some are just plain ridiculous: "I'm a cowardly fool!!!11!"
: "Oh, I know what the ladies like."
: "To war"
: "Bam! said the lady"
: "Hey, uh, Captain? Ding-a-ling!"

: TL;DR Though the deadline's past, I have someone who runs yearbook and he'll
: slip in a quotation revising as an inside job. Though now I ask if anyone
: has any great, inspiration, yearbook-fitting, Halo-related quotation
: they'd like to share, and for me to subsequently use?

: "One final effort is all that remains", but I have confidence for
: the weeks that follow.

: Thank you, everyone, really.

I hate to be a downer but maybe this is a time to use something more fitting even if its not Halo related? It might be better to use something that means something to the people you graduate with than to really search for a Halo quote that sort of fits.

That said no doubt the people from here can come up with something that works well!