Way too many, but there's at least a hundred I'd choose over Citizen Kane. Here's a handful from a full-fledged TCM addict, in no particular order:

Casablanca
Best Years of Our Lives (probably my #1)
Modern Times
Manchurian Candidate
12 Angry Men
Grapes of Wrath
Shadow of a Doubt
Battleground
Blackboard Jungle
Paths of Glory
To Kill a Mockingbird
Sunset Boulevard
Dr. Strangelove
Double Indemnity
Cat People
White Heat
Duck Soup
Gaslight
A Hard Day's Night

Cabinet of dr. Caligari.
Amazing scenery!
It's public domain in big part of the world, so if anybody wants to watch it, check it out!

Excellent choice!

Yeah, too many to remember, but you should watch Following.

Oh, and Harvey :D

+1

Well its not the best movie in the world, not the best BW movie anyways - yet the Call of Cthulhu came to mind in first.

Probably Faust (1926)

The Fighting Seabees, Casablanca, and Roman Holiday come to mind.

Raging Bull

Oh hell... It's hardly a category. Like "what are your favorite movies which titles end with a consonnant".

Anyway, as some personnal faves, I'd say :

- Le cave se rebiffe
- Casablanca
- Twelve angry men
- Hotel du Nord
- Monsieur Verdoux & The Kid
- A day at the races
- Citizen Kane worked on me too, although I haven't seen it for a very long time.

Well, call me unoriginal: Citizen Kane.

Hm, there's a couple of notable b&w movies I could mention:

Wild Strawberries (Bergman, 1957)
12 Angry Men (Lumet, 1957)

Horror: The Last Man on Earth
Sci-Fi: The Day the Earth Stood Still
Christmas: It's a Wonderful Life
Comedy: Abbott and Costello Meet Frankenstein

It is getting harder to tell which are black and white movie these days, they are getting pretty good at colourizing them. I know I have seen a few that I think of as being in colour which are actually black and white movies.

I wonder if they will ever colourize Clerks. It would be weird if they did, but I somehow think they probably will some day.

Schindler's List, if that one counts - I think there's one scene that uses colour in a very limited fashion. If it doesn't, The Great Dictator.

[in a creepy voice] They're coming to get you, Barbara!

I can't believe that nobody listed this movie.

They're coming for you, Barbara!