Well I've seen 13 movies off the list... and I'm willing to bet my husband has seen the other seven that I haven't (between the two of us we are a super geek). But then again I am also a BIG movie buff and have seen/own a ton of other movies as well.
But I think the real issue with this list is is that the definition of 'geek' is not really given and is a difficult thing to peg down. There are lots of different kinds of 'Geeks' out there really.
This list seemed a little more geared toward 'computer/scifi geeks'
I know that for a group such as ourselves I would have more more fantasy/Medieval films.
Dragonheart
Men in Tights
Robin Hood (Kevin Costner)
Rob Roy
Highlander
Braveheart
How to Train your Dragon
Princess Bride
Then, like someone mentioned earlier, there are more adventure geeks. And I'll put their two recommendations here as they were excellent:
Indiana Jones
The Mummy
Boondock Saints
Die Hard
Snatch
Lock Stock and Two Smoking Barrels
Fight Club
And of course there are also comic book geeks and all the comic book movies are too many to mention here but I will plug my favorite - Hellboy because I can.
And you certainly can't leave out some of the Scifi classics not listed on the boardgamegeeks list such as Tremors...
Geekdom has many faces, and in the end you really have to tailor your own 'must see movie list' to go with what you and your friends are constantly quoting and referencing while gathered in some geeky social situation
M.