I'm going to heartily agree with Sieck that Life of Brian is 
The Best MP film.  I could easily see a case being made for Meaning of Life or Holy Grail, though I would still disagree.  I don't think I know what the other one is...
I just love the combination of history, theology, ridiculous humor, and scathing satire.  Holy Grail's got the period aspect, but doesn't have christianity as its main target.
The way they use the character of Brian too just speaks volumes of truth about all kinds of shit.  But mostly I like it for the silly lines.  "I've been here five years, they only turned me right-side-up last week!"
"spare a talent for an ex-leper sir?"  bwahahahaha!
X-leper Alms for an ex-leper. Bloody donkey owners. All the same aren't they.
   Never have any change. Oh, here's a touch.
--------[Brian and his mum walk along the street.]
   Spare a talent for an old ex-leper.
MC   Buzz off.
X-leper [Still following] Spare a talent for an old ex-leper.
MC   A talent? That's more than he earns in a month.
X-leper Half a talent then.
MC   Now go away.
X-leper Come on, bignose. Let's haggle.
Brian   What?
X-leper All right. Cut the haggling . Say you open at one sheckle, I start
   at two thousand, we close about eighteen hundred.
Brian   No.
X-leper Seventeen-fifty?
MC   Go away.
X-leper Seventeen-fourty.
MC   Look. Will you leave him alone.
X-leper All right... two sheckles. Just two. Isn't this fun, eh?
MC   Look. He's not giving you any money, so piss off.
X-leper All right, sir. My final offer: Half a sheckle for an old ex-leper.
Brian   Did you say EX-leper?
X-leper That's right, sir. 16 years behind the bell, and proud of it, sir.
Brian   Well what happened?
X-leper Oh, cured sir.
Brian   Cured?
X-leper Yes, a bloody miracle sir, God bless you.
Brian   Well who cured you?
X-leper Jesus did, sir. I was hopping along, minding my own business. All of
   a sudden, up he comes, cures me. One minute I'm a leper with a trade,
   next minute my livlehood's gone, not so much as a buy your leave...
   You're cured, mate. Bloody do-gooder.
Brian   Well why don't you go and tell him that you want to be a leper again.
X-leper Ah, I could do that, sir. Yeah, yeah. I could do that I suppose. What
   I was thinking was I was going to ask him if he could make me a bit
   lame in one leg during the middle of the week. Y'know, something
   beggable, but not leprosy, which is a pain in the arse to be blunt,
   excuse my french sir, but...
MC   Brian. Come and clean your room out.
Brian   There you are.
X-leper Thank you, sir, thank... Half a dinari for me bloody life story?
Brian   There's no pleasing some people.
X-leper That's just what Jesus said, sir.