This one's really for Bitt, but I'm sure everyone else will chime in, as well.

Which of the following phrases is correct (and why):
"all of a sudden"
or
"all of the sudden".

I know which one *I* think is correct, but there still seems to be some doubt in some peoples' minds, even after pointing them here, which is the best I could find on the 'net.

Any better explanations out there?