Probably not yet 20, but:
Jaws.
Over 20 times:
Trainspotting
Persuasion (with Amanda Root/Ciaran Hinds)
*Notorious *
*A Room With A View *
The Commitments
Best In Show
*Sense & Sensibility * (w/ Emma Thompson)
*Pride & Prejudice * (with Colin Firth in hot white wet shirt 
*The Princess Bride * (played constantly when worked at video store, along with Clue. Safe to watch and infinitely quotable) Probably watched those two movies at least 300 or more times over two years.
And… *The Battle for Endor/Ewoks Movie * - not by choice but because my little brother, who I constantly had to babysit- would only be manageable if we let him watch it. Must have lost count at about 200 times…
The Vikings was my favorite movie for longer than I like to admit. Love the music. Do-DOOOO-Do, Do-DOOOO-Do.
Probably Dinner for One. I seem to have seen it on television each New Year’s Eve for at least the last 10 years.
Raiders of the Lost Ark (saw 13 times in the theaters, many more times since)
Singin’ in the Rain
Double Indemnity
Beauty and the Beast (Disney version)
Princess Bride
My Favorite Wife
Shall We Dance (Astaire/Rogers version)
both Toy Story movies
Notorious
My Man Godfrey
Philadelphia Story
Holiday Inn
White Christmas
The Court Jester
The Lady Eve
The Little Mermaid
Yankee Doodle Dandy
and not movies but I’ve seen How the Grinch Stole Christmas and A Charlie Brown Christmas at least 39 times (once a year since I was born).
It would have to be any of these:
Oklahoma
Carousel
The Wizard Of Oz
Miracle On 34th Street (the original)
A Hard Day’s Night
Help!
Magical Mystery Tour
Yellow Submarine
Let It Be
The Nutty Professor (the original)
The Disorderly Orderly
A Christmas Story
Galaxy Quest
Evolution
The Princess Bride
Predator
Dazed and Confused
It’s a Mad Mad Mad Mad World
Ferris Bueller’s Day Off
Breakfast at Tiffany’s
That’s one strange group of movies.
Planes trains & automobiles
When Harry met Sally
Money pit
Blues bros.
Groundhog day
Midnight run
Defending your life
Stir crazy
Shawshank redemtion
Young Frankenstein
Ghostbusters.
Rocky Horror Picture Show.
Phantom of the Paradise.
Wizard of Oz.
I haven’t really kept track of how many times I have watched my favorites, but I can say with absolute certainty that the following have been viewed by me at least ten times:
Back to the Future (all three)
Rain Man
Planes, Trains and Automobiles (it’s a pre-Thanksgiving tradition with me)
National Lampoon’s Christmas Vacation (also a holiday tradition)
Falling Down
The Matrix
Lethal Weapon 1 and 2
I forgot all about A Christmas Story, Amadeus, and Time Bandits. Wore out those videotapes.
OOOODDDIINN!OOOODDDIINN!
Rocky Horror, hands down. Well over 100.
Distant second is A Knight’s Tale. I can resite the dialog, if that tells you anything.
Runners up: The LOTR trilogy , the original Star Wars (probably saw it 20 times in the theatre!), Wizard of Oz…
The only movie I have currently watched probably 20+ times (I lost count somewhere after the 12th time) is Young Frankenstein.
The movies in 2nd place would who will likely make it to that mark eventually are The Princess Bride and Monty Python and the Holy Grail.
The LOTR trilogy will eventually work it’s way up there but as much as I like them, I’ve probably watched them barely 5 times each.
There are some movies I will watch when they come on television but I don’t own them or plan to buy them; those are A Christmas Story, The Shawshank Redemption and Jaws.
My list:
**A Man for All Seasons
Spartacus
Forbidden Planet
2001
King Kong
**
A lot of my favorites aren’t on the list, because I didn’t get copies until recently. I’m sure if you included all the movies I watched, a lot of the ones i saw as a kid would show up more than recent favorites, including:
**Seventh Voyage of Sinbad
Abbott and Costello Meet Frankenstein
The Beast from 20,000 Fathoms
Mighty Joe Young
A Funny Thing Happened on the Way to the Forum
**
A Clockwork Orange
Shawshank Redemption
Bottle Rocket
Midnight Run
Bloodsport
Shawshank Redemption
To Sir, With Love
Twister
The Abyss
Are you sure you haven’t just watched it once, repeatedly?
The movie I’ve (willingly, excluding stuff the kids put on) watched the most is, I think, Amelie, or maybe The Fifth Element, but in either case, that’s not hundreds of times; probably not even twenty.
Forgot another one – Honey mentioned Twister, which reminded me of Tremors.
When I was a wee one, we played a game in the house where we couldn’t step on the floor because something would get us, so we’d go from room to room, walking on furniture and hanging from whatever might support our weight.