I have a few that I use on a regular basis.
If we're -my friends and I- are out and about driving around, and we happen to be in behind a few slow cars; I always like to shout, "Fly, you fools!"
The most common amongst us all of course, is the, "You Shall Not Pass!" phrase which I like to imitate -as best I can - Ian McKellan when I see a
'No Passing Zone' sign and nearly cause us to wreck.
Whenever I'm frustrated with something or someone I say, "Go back to the abyss.." or was it shadow in the movie? I can't remember.
I like to call our bridge the 'Bridge of Khazad-Dum'. So whenever we're leaving to go somewhere I always say, "To the bridge of Khazad-Dum." in Ian McKellan's epic voice. I fail miserably at trying to imitate him
The other one I use frequently is whenever someone asks me where I'm going, I always say, "I'm taking the hobbits to Isengard!"
The Poe-Tay-Toes has become the only word I will use when speaking of taters now; and it HAS to be said the way Sam says it or it loses it's appeal.