Doc: "Great Scott!"

Clara: "I believe you've underestimated me, mister."

Jules: "You upstart, overgrown mass of immature parasitic lifeform!"

Verne: "You do sorta look like that J. Michael Fox guy."

Marty: "This is heavy!"; "Nobody calls me chicken!"

George: "Last night Darth Vader came down from planet Vulcan and told me that if I didn't take Lorraine out, that he'd melt my brain!"

Lorraine: "That's your name isn't it? Calvin Klein? It's written all over your underwear."

Jennifer: "I'm old!"/"I'm young!"

Biff: "What are you lookin' at, butt-head?" "Hello, is anybody home?"

I love the "Great Scott" and "This is heavy" catchprases.

For George, I prefer: "I am your density... I mean, your destiny."

For the Tannens, I like: "Well, lookie what we have here!" I had Griff Tannen use that line in Time Switched.

Another one of Marty's favorite sayings is "HOLY SHIT!!"

Another one of my favorites for Doc is "Ronald Reagan? The Actor?"

Marty does say "holy shit" a lot, doesn't he? That's part of why I was so worried when FFN went through phase of censoring swear words. I'm not especially a fan of swearing, but it would almost be out of character for Marty to not use that phrase.

Did you notice that, in the first movie, 1985 Doc never says "Great Scott?" His first instance of using that phrase in the movie is when (in 1955) he says, "1.21 gigawatts! Great Scott!"

I never noticed that.

My fave quote from the first movie:

Marty: Gimme a tab.
Lou: I can't give you a tab unless you order something
Marty: OK, gimme a Pepsi Free.
Lou: You wanna Pepsi pal, you're gonna pay for it!

Oh, yeah! I love that one! That's a classic. Of course, I also love all the "Mom, is that you?" scenes.

Needles: Hey! The Big M! How's it hanging, McFly?

Spike: What's wrong, McFly? Got no scrote?

Marty: What if I came back to the future and I end up gay?
Doc: Why shouldn't you be happy?

Goldie: Mayor! Now that's a good idea. I could run for mayor.

I was laughing so hard when Doc and Marty reversed catchphrases in Part III.

Oh, yeah, and they actually switched role in other area's too. Also, check out those parallels:

Marty to 1955 Doc: Doc, I'm from the future. I came here in a time machine that you invented. Now, I need your help to get back to the year 1985.

Doc to Clara: All right then. I'm from the future. I came here in a time machine that I invented and tomorrow I have to go back to the year 1985.

Also compare this:

Doc: Marty, you gotta come back with me!
Marty: Where?
Doc: Back to the future.

With this:

Marty: All right, so that's why you've gotta come back with me.
Doc: Where?
Marty: Back to the future!

Marty: Nobody... calls me... Chicken.

(Nobody calls ME chicken either)

Aw yeah...

:marty: Great Scott!
:docs2: Whoa, this is heavy.

I can't stop laughing at your picture of Griff.

I made it myself, I never saw him smile

Marty to 1955 Doc: Doc, I'm from the future. I came here in a time machine that you invented. Now, I need your help to get back to the year 1985.

Doc to Clara: All right then. I'm from the future. I came here in a time machine that I invented and tomorrow I have to go back to the year 1985.

In a way, it's so bittersweet when Doc says that line to Clara - because the trilogy is so close to being over again. When Marty says that similar like to Doc '55, his adventures are just getting started.

You know you're a BTTF fanfic writer when you're not completely sad about the trilogy ending - because you know it's really still only the beginning of Marty's adventures.

It was a little sad writing the part in That '70s Story when Marty and Haven plan to use the time machine for the very last time, even though we know that Marty Jr and Harmony will get their hards on the time machine again just a little over ten years later. At least, Haven gets to take a bonus trip to 1997 with Marty '86 - even if it's not entirely fun and games.

Another thing that repeats itself...

At the beginning of Part I

Biff, to George: You realise what'll happen if I had in my reports in your handwriting? I'll get fired.

And in 1955...

Biff: You realise what'll happen if I hand in my homework in your handwriting? I'd get kicked out of school.

Hmm, I'll make a topic on this.

Doc: Damn! Where is that kid?

Doc: Precisely!

Marty: You bilt a time machine out of a delorian
Doc: The way I figure if your going to travel through time why not do it in style
(I think thats right)

Doc: What did I tell yo 88 mph

Ah, c'mon. The one catchphrase that really hits home is the one where in Twin Pine Mall, Doc says,

"At 88 miles per hour, you are going to see some serious shit!"

That's gotta be the classic line for all three movies...and of course the basis for a cool user name :D