Very influential and still powerful.

Four recent rug-out-from-under-you twist endings that I admire (but I wouldn't say they were superior to the ending of Diaboliques, and the movies themselves aren't as good either; ultimately I agree with the suggestion of your title):

eXistenZ

The Game

Fallen

A Beautiful Mind

Other notes:

We've already discussed Dead of Night, the ending of which has certainly been influential, as is the fact that it occurs during the final credits.

Another Boileau - Narcejac adaptation has a great twist: Vertigo. But I think the twist for Stage Fright is Hitchcock's best, just in terms of twistiness.

I'm not a big fan of the Usual Suspects twist. Once you've seen it, the movie isn't particularly compelling to rewatch. It's more gimmick than storytelling, to my mind.